Hulu and similar sites use advertisements that can't be skipped. Can't do that with HTML5.
Why not? You could encode the original video as multiple segments, in order to watch the next segment, you have to watch an ad. Maybe use some kind of long polling to ensure that the advertisement was watched in its entirety -- supply a unique key at the end of the 30 seconds that the client has to rehash. It's a relatively minor engineering challenge, but I'm sure it can be solved.
It's really quite easy to do with a bit of javascript magic and some backend work. Not sure why you'd think it's impossible.
I was attempting to be general and be the background voice which says "Well, if it can be done, it will be done"