Zeldman evangelised XHTML as head of the "Web Standards" movement, wrote the seminal "Better Living through XHTML" article, and was imho largely responsible for getting the masses to adopt XHTML1 - for no apparent reason.
But my point is it wasn't just "tyrannical" browser companies who thought XHTML2 was flawed, experts like Tantek and Mark Pilgrim, and even XHTML advocates like Zeldman, were equally unconvinced.
Your post portrayed the browser's companies decision to not support XHTML2 as some nefarious plot on their part, imposed on the rest of us. This was not the case. XHTML on the web failed (or perhaps more accurately, "fail on error" on the web failed).
You said above:
(X)HTML5 is backwards compatible, XHTML2 isn't.
So HTML5 can be adopted gradually/progressively as browser support for individual features is added (like XMLHttpRequest has been adopted), but XHTML2 required a year-zero, all-or-nothing approach to adoption.