It would be good for Microsoft to have more internal studios. They only seem to have Forza, Halo, Gears Of War and Fable every year now. And Rare reduced to making Wii Sports clones
. They're doing well by having best-selling versions of multi-platform blockbusters at the moment. But if they lose that advantage in the next generation, they'll need some exclusives to fall back on. Sony and Nintendo have a huge portfolio of exclusive games from first-party studios, but Microsoft doesn't. It could hurt them in the future.
Also, the new Tomb Raider looks good.