@endimion:
The Cell is jointly developed by Sony, IBM and Toshiba, so I think ( well, I would bet on it ) that they all share some of the IP and get a share of the IP licenses ;)
The same counts for HDMI, but there are more companies involved ( Sony, Hitachi, Matsushita, Philips, Thomson, Toshiba and some others.
However, controlling / possessing ( parts of ) the IP always gives the advantage over competitors and can be very profitable, even if the competition sells more devices with your technology (that is, as long as they pay for the IP-licence)
And I don't think MS would really want to go into the electronics, they would more likely create a software-based business-model around the online media capabilities, but a software-model alone would not get them there.
Besides, Sony has a better brand and more experience in consumer electronics, people mostly think of computers / windows when they hear the name "Microsoft".
But with Sony, they think about TV / Video / Audio and Playstation. ;)