In most cases it doesn't really matter. MS get to spend some money, publisher sells more games on x1 platform. And to top it all off they then sell even more on the PS4.
The problem is with games like COD. Giving the dlc much later to PS than Xbox hurts them. A lot of PS people just stop caring and stop getting the dlc.
You have a point that they might lose more potential sales from the ps4 than they gain from the x1 but i'm pretty sure the MS money covers that.
The thing you should be saying is, that 3rd party advertising is gonna get way more expensive for MS now. They have way less pulling power.







