It doesn't really matter what you think of the iPad itself, because love it or loathe it, it will irreversibly change the landscape of the App Store. Here's how.
Apple Will Finally Have to Fix Fragmentation
Fragmentation in the App Store is a problem already. Even across devices with the same screen size, same core feature set and same product name, you find subtle differences in capability. A first-gen iPhone doesn't have a compass, so it can't run augmented reality apps. A second-gen iPod Touch can support mic input, while my first-gen model—purchased just a few months before—can't. An iPhone 3GS will run a 3D game like N.O.V.A. beautifully, while a regular old 3G struggles to keep a viewable framerate playing Sonic the Hedgehog.
Part of the current problem is the lack of division between products in the App Store. Developers generally say what kind of device is supported in obvious cases—a compass-based app will most of the time be listed as 3GS-only—but there's almost no enforcement by Apple, meaning that it's easy to download an app that you can't really use. It's getting to the point that there needs to be separate sections for each device, or some kind of rudimentary search or sort parameter for filtering out incompatible software.
We've needed a fix for fragmentation for a while, and hopefully the iPad, being such an obviously distinct device, will give Apple the kick in the ass they need to implement one. The iPad may run all iPhone apps, but the iPhone will not necessarily run all iPad apps, so assuming downloads aren't required to be packaged together as dual-mode iPad/iPhone apps, there will have to be a way to prevent purchasers from accidentally purchasing something they can't use at all on their iPhone. An improved, properly segmented App Store storefront or download system is inevitable; we'll just have to wait and see what it looks like.
Data Will Be Freed
In some iterations, the iPad is a 3G-capable device, and in all, it has a microphone. What it never has is built-in voice capabilities—that is, unless you download them. According to early reports, the new iPad and iPhone SDK has lifted the restriction on voice calls over 3G data (VoIPo3G?). Opening up voice over data services for the iPad could have a larger effect on iPhone apps than on iPad apps, since, you know, they're for phones.
AT&T isn't the first wireless company to allow voice over 3G data, and the iPhone is far from the first phone to support it, but for both to now be onboard with a technology that threatens a core feature of carriers' business plans is a very, very good sign.
In-App Purchasing Will Finally Take Off
The iPad will ship with a book store, but what about all those fancy magazines? (Or to adopt their parlance, "WHITHER THE PERIODICAL?") If print publications were placing their future success in Apple's hands, Apple's just handed it right back. Unlike books, which will be sold directly through an iTunes-style storefront and viewed through a common interface, magazines and newspapers will be in charge of selling their own apps, with their own interfaces, and their own business models. But this could turn out to be a good thing.
Imagine an icon on your iPad. When you tap it, it'll open up your favorite magazine, in full color, with magazine-style formatting and interactive content. The app itself is free, but the content is not—new issues come either individually, at newsstand-ish prices, or through a subscription. They will compete with one another to provide the best e-magazine experience. Unique, miniature storefronts, selling content for anything from a single publication to an entire publishing empire: this is the kind of thing the App Store's in-app purchase system was made for.
What's funny about this is that in-app purchases are still App Store transactions, carried out through the same payment system and with a portion of revenues set aside for Apple. Nothing will change except the packaging, but that alone will be enough to fundamentally change the App Store economy, and how we pay for print content. (Increased dependence on in-app purchases could help stem the tide of piracy as well, but that's another discussion entirely. Soon!)
Note: Apple may be faced with some resistance in this model, though, since magazine publishers would much rather handle billing themselves, if just for the valuable data they could glean about their subscribers.
"Apps" Will Grow Into "Applications"
Apps are small, they're simple, they've got a short title. They're like applications, but nuggetized. And that's fine! We call software on phones by a different name than we call software on PCs, because something about the products feels different. The iPad could bridge that gap.
The SDK has been out for less than two days, so nobody has had time to really delve into the app potential of the iPad. Except, of course, Apple. Steve Jobs spent what probably seemed like too long on iWork for the iPad, a set of $10-a-pop apps that Apple fully redesigned for the iPad's touch interface which are an order of magnitude more complex than anything on the iPhone right now. (Our friend John Mahoney at PopSci goes so far as to say these are a sneak preview of Apple's entire future software philosophy. He could be right.)
Of course, these are Apple apps, so you'd expect them to be executed well, and to use Apple's device to its maximum potential. But with more screen real estate, more power, serious text entry abilities and a more mature SDK at their disposal, the developers are going to give us apps of an entirely new caliber, not just a new size.
Apple Will Rule With an Iron Fist, Or Learn to Let Things Go
With iBooks, Apple is setting itself up for an awkward situation. Apple has strict (if sometimes inscrutable) rules about what types of apps are permitted, mostly concerning appropriateness of content and the safety and stability of the app's code. The prohibition that always rubbed developers and customers the wrong way, though, is the ban on apps that duplicate the functionality of Apple's apps, like email clients, new browsers, and by extension, alternative music stores and app stores. These are now joined by iBooks, which is unique in that its actually invading territory inhabited by preexisting apps, like Amazon's Kindle app and indie favorites like Stanza. So what does Apple do? Do they purge Kindle and co. from the App Store, or mark ereader apps as incompatible with the iPad? The Kindle app is to iBooks what an Amazon MP3 store app would be to iTunes, all the way down to the competing file formats and DRM systems (iBooks renders a proprietary type of ePub file, while the Kindle sells books in a proprietary AZW format), so even if this would be a terribly dickish thing to do, it's possible.
The more likely path is a continuation of the gradual erosion of Apple's tight grip on the App Store. Along with explicit, proactive feature additions like the ones we saw in OS 3.0, Apple's been letting more and more types of apps slide through the approval process. The Rhapsody app may not provide a plain music download service like iTunes, but it is music that you pay for, in an app that doesn't come from Apple. you may not be able to download a browser with an entirely new rendering engine, but now you can download a cornucopia of alternative browsers that render through WebKit. Some apps can stream video over 3G now; others can broadcast voice communication over AT&T's data network. It's too early to presume, but if iBooks doesn't murder its competition, Apple could be charting a course toward a more open App Store, not a more tightly controlled one.