More likely the infamous DRM!
Have had several TV's with builtin hard drives come through the shop and because of DRM they will ONLY record from standard NTSC Cable.
Haven't had a chance to test them with Over the Air HD as to date it's almost nonexistant in Canada, might record from that. Cable boxes and Sat Boxes poll the video out and will not send a signal to a "Recording Device".
Even if hooked up with Component Video the builtin DRM in the TV prevents recording of HD.
On an upnote however, Shaw's boxes will record 3D.
Thank the Ambulance Chasers yet again!