It makes sense, since Ubuntu for smartphones is already finished, launched and matured.
Oh, wait....
As far as Windows taking a hit, it could have happened for as long as Ubuntu (and Linux-based OSes) have been out there. Nothing beats free, right? I use Ubuntu on some of my systems, I would switch in a heartbeat to it as my one-and-only OS, but there is this "slight" compatibility problem for a bunch of applications, not to mention gaming support being still in it's infancy. Searching the web for a compatible version of an application, then searching what repositories to add (and how), getting the packages and finally installing them is not exactly what general populace is looking for in an OS.