I think what we're seeing here is people no longer search for Facebook on Google; they have started going straight to Facebook, with no Google in between. For lots of folks, Facebook is the internet.
Try it. Type "facebook". Heck, on most folks' machines you can just type "f". It'll auto-complete the URL. If you want to actually google for "facebook" you'll have to type "facebook " with a space.
If you aren't sharing your browsing habits with Google or Microsoft, would this behavior show up?
Also, this won't show a 'change' in behavior over the last few months or a year because the address bar has acted as search for some time already.