That presentation wouldn't even have worked in the latest edition of Firefox.

But it is important to understand that you need an uptodate browser to view webpages today. Gracefully handling obsolete browsers is what got us into this mess in the first place (actually it was allowing anything less than completely correct pages -- you can't have syntax errors in your c code and expect it to compile, why should your HTML be any different).

Do you mean that the latest version of Safari on iOS 5, released a couple months ago, is an obsolete browser? It is amazingly easy to make a page like that work in every browser made since 1996. And it does work on Firefox, albeit very slowly.

Things like this presentation are the actual reason we got into "this mess". Making your pages accessible to everyone is a necessity. I don't mean to be impolite, but you need to revisit your concepts. HTML5 is all about gracefully handling mark-up errors in a consistent way, not the opposite. HTML is originally a language for authors, not programmers. You're thinking of XHTML vs HTML, and that's a completely different matter.

That depends on what features it supports, but a few months is quite a long time ago in browser development.

On the other hand ie9 is already obsolete.

And how exactly does HTML gracefully handle a lack of canvas?

Would the web have thrived if browsers only accepted perfect html?

I can't see why it wouldn't. A clear and simple error message would allow people to fix it.

No.