This is probably the most true statement in your entire comment.
Running with the assumption that of course we should ignore the users who aren't "most" users (not a safe one).... I'd go farther, though. Whether or not these users are getting access to the utility they're looking for through:
(1) a web page with some layer of interactivity on top of more-or-less legible document semantics or
(2) whether they get it through a giant-blob-of-code SPA
is also irrelevant, right? Except to some minority of power users who can actually get more utility when someone uses a more basic semantic-document resource-oriented approach.
So it isn't the users who are driving the "let's use the web as a VM for desktop apps!" trend. It's the developers. And it isn't the billions of Internet users whose habits would need to change.
I'd guess the most ready response to this would be something like "How would you have the current Facebook/YouTube/WebMail Experience without this Desktop-Experience-Focus?" But as far as I can tell, the essentially utility involved here -- and to a large extent, the best things about the experience -- haven't really changed since a FB page was actually a legible document (a milestone we left down the road a looooong time ago).
The document-centered approach does have its limits. There are some applications it will not support. First-person shooters.... sure, deploy a black-box binary to a runtime.
Facebook, YouTube, and web mail are not really in that category at this point, and developer choices are the primary thing driving the march away from documents here.