Anyone who was hoping for a built-in Blu-ray drive in their next-gen iMac is gonna have to wait till mid 2008. That's when Intel will replace their current Bearlake chipset with their Eaglelake chipset, which will officially support Blu-ray. Apple is infamous for waiting before they adopt new technologies, so in a sense this comes as no surprise. The question is, how badly do you want an integrated Blu-ray drive in your next iMac? Bad enough to warrant not buying one without a high-def drive?
Just to extrapolate a bit on what the first couple of commenters said: if it looks like Apple is gun shy about adopting this particular bit of technology, it's because the risk completely outweighs the reward. USB they could safely push because they could at least guarantee that Apple would have a ton of USB peripherals available, and that market just exploded. But nobody seems to know what's going to happen with Blu-Ray, and there's no obviously huge demand for it now.
Will it delay my purchasing a new Mac? No, the fact that I just blew a bunch of money on camera stuff will delay my purchasing a new Mac. :)