I wouldn't be surprised if the in-house development costs rivaled or exceeded what something like Windows Mobile cost to license.
That implies that Windows Mobile doesn't require similar in-house effort, on top of the OEM license fees. Windows phones still require the same hardware driver development effort, and WM7 is already starting to receive the carrier-bastardization treatment. I'd say Android's licensing being free is the only difference.
Android OEMs have to develop their own drivers to get the various components (screen, GPS, WiFi, Bluetooth, 3G radio, accelerometer, etc.) working whereas with WP7, Microsoft will provide all the device drivers. Part of this can be attributed to the fact that Android devices have a much wider range of hardware options, so it's a lot more difficult to have an uniform set of drivers.
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.
That implies that Windows Mobile doesn't require similar in-house effort, on top of the OEM license fees. Windows phones still require the same hardware driver development effort, and WM7 is already starting to receive the carrier-bastardization treatment. I'd say Android's licensing being free is the only difference.