Here is another reason why mobile operator may support Windows Phone in preference to Android.
According to network equipment provider Ericson, in their November 2013 Mobility Report, the average Android user used 2.2 GB per month of mobile data, while the average Windows Phone user only used 1.4 GB.
iOS was in the middle, with 1.7 GB of monthly mobile data usage, indicating that the volume of data used does not necessarily correlate with the volume of apps available.
Ericson instead correlates it with the operating system itself, with one explanation being background services, which are pretty unmanaged on Android, and may therefore easily use excessive amounts of data. Windows Phone is by comparisons a more closed OS designed to use data more sparingly, and with network capacity at a premium this would be one more reason for carriers to encourage new users to adopt Windows Phone rather than the more wasteful Android handsets.
See the report here (PDF).