Another issue is Microsoft does not have profitable consumer services other than Xbox. Even Microsoft can integrate a lot of its services with Windows Phone, it is a big money sink until Microsoft can make profit on search, maps, outlook.com, skydrive, etc. They have tried for over a decade by now.
In the end, I really like to see 3-way competition between Apple, Google, Microsoft.
The only way for Microsoft to entice carriers is to bend over backwards with deals, promotions and letting them customize the phone. Which was exactly what Microsoft was trying to avoid by copying the "we're calling the shots" way of Apple.
The other option, of course, is to make a phone that is so desirable that customers will start demanding it. So far, WP8 is not that phone. Partly because it's _not_ so much better than iPhone or Android, and partly, perhaps, because people's not so positive association with the Windows brand ("isn't that the thing that always needs updating?").
...but that's price fragmentation, not a commentary on the 'cohesiveness' of the Nexus 4, which is a brilliant device.