That makes HTML5 harder to implement, not simpler.

HTML5 != XHTML. (If that's what you're saying.)

HTML5 breaks soft. It's easier to write, which is what drives content. A parser for which there is no content becomes moot.

(I'd prefer far more rigorous document specification. That's not the Universe I inhabit.)

You're responding to a thread pointing out that browsers are too complicated to implement, which has forced everyone but Google and Mozilla to give up on providing browsers and web standards.

And Google is currently the funding source for Mozilla, giving them a more or less complete monopoly on the future of the web.