That was the situation prior to the writing of the HTML5 spec, not a situation it created. The majority of the web was not, and never would have been parsable a

That was the situation prior to the writing of the HTML5 spec, not a situation it created. The majority of the web was not, and never would have been parsable as strict XHTML, whatever the desire of the W3C or anybody else. And even for new content, the idea that every hand-authored file would be well-formed, or that every half-baked and buggy CMS would always produce correct markup was a pipe-dream. If strict parsing had been enforced, we'd have a web where a large proportion of the sites you visited each day would be broken. Or rather, we wouldn't, because complaints from users would have long ago forced browser vendors to implement graceful error handling, and so you'd end up with something akin to HTML5 anyway. Indeed, it was encountering precisely this problem that made vendors like Mozilla and Opera (who, incidentally, never had billions of dollars) to lose faith in XHTML in the first place, not some masochistic desire to keep their browsers' code as complicated as possible.