It seems to make no sense. A studio is just a collection of individuals who work as a team, so bringing them into the corporate Microsoft world could do more harm than good. There is another way and that is to sign up good studios for exclusives. This would cost a lot of money but a lot less than buying them. It also allows for much more flexibility.
Of course this article is prompted by the news that Bungie have done a buyback of the company from Microsoft. You would wonder why Microsoft bought it in the first place when they could have just paid them to do the Halo series. Just as they will now, presumably, pay them to produce more exclusive 360 content.
Also you must look at Rare. This cost Microsoft $377million. You really must wonder if this was value for money. Or, more importantly, what they could have done if they had spent that $377m in other ways.
So do you think that studios work best when they are independent? Or that Bungie are fools to cut the safety net that Microsoft provides?