They bought Kinect from another company – the hard work of getting approvals and resources and everything else to start on it had already been done outside of Microsoft.
It's definitely an impressive bit of tech, but would it have been possible were its genesis subject to the byzantine internal politics of Microsoft? I dunno. I wouldn't put money on it.
the hardware was licensed from another company, but the body-tracking software was developed in house (by a small incubation team in Redmond working with researchers at MS Research's UK office). the whole product definition as well.