what would be the return on investment to get away from Flash? Adobe's tools are very mature making development easy. HTML5 tools would need to be just as mature or you're going to spend a lot longer coding the same functionality. and they will have their own issues, bugs and it will take the developers time to learn them.
if anything is going to kill flash it's Microsoft's Silverlight. and i haven't seen any games using silverlight. tens of millions of people use flash for games like farmville.
What return? Oh I don't know, more ad revenue?
HTML5 is mature, it is based on what the web has been using since the early 90's. HTML5 isn't new, it is an improvement on what every website in existence is using.
It doesn't take long to code the <video> tag. While of course this would be a tad more work, this isn't going to take long to implement.
If you are saying the Hulu developers don't know HTML, then I am surprised they can't put anything together at all. These people know Web Design, which is why they were put on such a large project in the first place. This isn't some starving artists website who can't code anything and use Flash instead.
Point being, I can only imagine that the Hulu project team doesn't consist of Flash developers. Given that the only major Flash component used is the video player.