But Microsoft made an active decision to integrate WP7 with Facebook. Beyond that their marketing for the phone revolves entirely around social {or more accurately keeping up with your social network without spending your whole life doing so)
CNN even had an article entitled "WP7 is the real Facebook Phone" (http://articles.cnn.com/2010-10-15/tech/windows.phone.facebo...)
Put another way WP7 is to Facebook as Google Services are to Android. There might be a few rare individuals who use Android but don't have a gmail account but those people are by far the exception.