Seeing as the rise of YouTube and Google video has pretty much made Adobe's Flash the de facto standard for Web streaming, you'd have to be a fool to try and introduce a browser plug-in for a new format. Either a fool, or a company with deep pockets. How deep? Try "This is madness! This is Sparta!" deep. Yeah, it's Microsoft.
Their Silverlight plug-in, which works not only with IE, but with Safari and Firefox (ha ha, Opera users) and essentially provides a browser plug-in that lets everyone stream WMV files like they do with flash files.
The improvement upon flash—and this is why people would want to use this instead of Adobe's—is that it's high-def. We don't have to explain to you how much better it would be to stream high-def TV shows from NBC or ABC if you missed them when they first aired. And with MLB, Netflix and others already supporting the format, Microsoft may already have some hope of dethroning flash.
Video introduction [on10]