I think it makes sense oddly. This also opens up MS to ship games for the DS, like Halo, or Rare games even. I think MS is saying "Lets topple Sony together, then worry about each other after the dust settles." Obviously with Sony holding 66% of the market, it's a sound business plan. They're not trying to take that 15% from Nintendo, because they know they never could. And even if they did, they're still miles behind Sony. What's much easier is cutting into the bloated Sony userbase and taking a chunk of that.