That last assertion is heavy speculation. Why are we assuming that, had XHTML been the dominant infrastructure, Facebook and Google wouldn't still be the best a

That last assertion is heavy speculation. Why are we assuming that, had XHTML been the dominant infrastructure, Facebook and Google wouldn't still be the best at leveraging it? And if anything, Google desperately did and does want people to semantically annotate data. They're extremely confident in their ability to be the best at organizing it, and well-annotated clean data is a huge benefit to them.