All current Windows Phone 7 devices are restricted to the Qualcomm QSD8x50 platform, so there isn't much customization to be done as the hardware is nearly the same for every vendor.
As far as I understand it, Windows Phone 7's API is Silverlight with a few restrictions related to screen size and the like.
I haven't coded anything for Windows CE, but making a Silverlight app for Windows Phone 7 is about a difficult as making a WCF app for Windows, or an ASP.Net app for the web.
Microsoft did a tonne of heavy lifting to make it so. There were boxed in drivers for virtually everything, and customization was absolutely minimal.
And when you bought a MotoQ, it was stock CE.