[amadiver]

Right on - they care about viewing the content. So if YouTube switched to <video>, over night, tons of users would switch browsers. Except that's never going to happen. My guess is that YouTube might serve up content using the <video> tag if the user isn't using a modern browser, and Flash content if they're using IE. I can't see them making such a reckless business move ( some users wouldn't/couldn't switch browsers, and there goes millions of paying customers ["paying" in that they view the ads]).

With companies like Google playing it conservative ( as all web devs do ), and adapting content to allow IE users to view it, there's not going to be an incentive for users to switch browsers.