I can't see one system doing it and not the other; especially if both want great third party support.
It's either both or none.
If just one does it, then people won't get that system. Pretty sure MS/Sony is smart enough to see that. Who knows though...
If MS plugs it as the entertainment hub box, maybe they can try to soothe consumers with all of its bells and whistles to handle the massive tumor it's carrying with it.