First, the HD files are more like 1.5GB. And ABC and Fox both use 1280x720, just like iTunes. It's HD. Both have AC-3 soundtracks. But there are differences:An hour TV show that is rougly 500 mb is not really HD. It is all about the mpbs. For example, eyeTV recordings are roughly 5 - 7 GB, and the mbps is 13 - 19, whereas the iTunes downloads are less than 2 mpbs.
- iTunes HD also has stereo AAC soundtrack, for playing the file on your computer (makes it bigger)
- OTA HD uses MPEG-2, iTunes uses H.264 (makes it smaller)
- OTA HD can go up to 60 frames per second, iTunes is 24 (makes it smaller)
Not a coincidence that AppleTV's max supported resolution is 1280x720 @ 24fps. This also means that all the HD shows (so far?) were originally shot on film.