It's extremely expensive to maintain a first party studio and MS is actually casting many of theirs off in favor of publishing a third party title, which they might feel is cheaper to do and more beneficial in the long run.
Either way, MS will constantly be funding and publishing third party titles, as opposed to Sony & Nintendo, which rely heavily on maintaining their own first party studios.
It's a very different business model and given the state of many studios today, may actually be a new way of profitably operating in this business (funding a title and publishing it has to be a cheaper way of doing business than completely owning your own studio). It's almost like they're trying to move to solely outsourcing their exclusive game titles.
Time will tell who has the correct strategy but don't worry about MS not having first party titles. After the breakup of Ensemble (a damned fine developer), it's obvious where MS plans to go down the road. I'm not sold on the idea but it is an interesting one, especially considering how they've had premiere third party developers (BioWare & Epic, for example) make exclusive games for the 360. On the upside, MS will constantly be searching for new IP and introducing top-shelf innovative software through third parties. On the downside, they will never have complete control over their "franchise" IP (like Mario, God of War, etc.)
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