I don't know where you get your information from, but Blackberry has broken compatibility in the last 3 OS releases, and Windows Phone 8 doesn't even run the same kernel as the previous version (breaks compatibility). I'm not sure if you ever touched Java ME back in the day... but yeah. You're just wrong on this one.
>Windows Phone 8 doesn't even run the same kernel as the previous version (breaks compatibility)
Windows Phone 7 apps run fine on WP8. Anyway breaking compatibility is a tad different from fragmentation. If your app runs on a WP7 phone, you can be reasonably certain it runs on all other WP7 phones. With Android, you can easily run into device specific bugs even though the version is the same and thus you're forced to test on the real hardware devices.
