These kind of games do make a lo of money. But I can't say I'm much of a fan of them. In one way they help to keep a franchise alive and might even bring new fans into playing the Xbox game (which is really great). But these games can also make companies focus on monetization more and forget developing great AAA games which is a really sad thing especially if single player is your thing.

A Gears Of War based strategy game (like Halo Wars) for PC and Console on the other hand would be amazing and welcome addition IMHO.