Microsoft probably hasn't done anything, because there's not really any motivation to do anything. I don't get the impression that baseball games are that big in terms of sellers, and outside of a community like this, it's certainly not going to be a system seller.
Plus, getting something anywhere near the quality of what Sony's baseball game has become would probably take a significant time, and financial investment, one that's not likely to produce results that make it a good business decision anytime soon, if ever.