Yes however the Xfinity app was compatible with my 'Device' when I was on stock.
Keep in mind that CM7 is based off the Android 2.3.3 OS for another phone. Someone had to take a copy of the OS and hack it so it would run on the Ascend. The market may be seeing that difference and think you are running something other than the Ascend.
Have you tried to log into the web version of the market and see what it shows as your phone/OS?