Not completely sure about situation and probably can't help much, but are you streaming the files to the WD unit?
I normally record Over the Air shows in High Def. on my Home Theater PC. When I stream them to my PC with Windows Media Player, they only stream at 2 MBps. If I stream them using Windows Media Player, they stream at 15-20 MBps. Window Media Player probably has the rights and setup to allow streaming certain types of content at higher resolutions. Not sure if something like this is involved in your situation, but it is a possibility.