HTML5 is a markup language, not a streaming transport. Apple used HTTP Live Streaming, which is tech they're trying to push as a new standard. It has certain technical benefits:

http://en.wikipedia.org/wiki/HTTP_Live_Streaming

I believe the VLC nightly build has support for it, but Apple's not going to go out and tell people "Hey, go use this weird beta client to access the stream."

Sort of like Gmail with the invites. Artificially restrict access, so you don't need huge scale from the get go.