I'm not really terribly concerned - MS's dominance over the gaming field is not nearly entrenched or large enough for them to muscle like this.

Remember, there is one direct equivalent platform for developers and publishers: PS3.

There is another that targets the same demographic, but smaller: PC.

There's also the wide open field of gaming in general, which is being dominated by Sony, Nintendo, casual game producers like PopCap, and increasingly social game makers.

MSFT has done extremely well with the Xbox, particularly Xbox Live, but they're far from the dominant player in this industry, much less a monopolist.