relating to Apple TV, this is what Apple says:
Video formats supported: H.264 and protected H.264 (from iTunes Store): 640 by 480, 30 fps, LC version of Baseline Profile; 320 by 240, 30 fps, Baseline profile up to Level 1.3; 1280 by 720, 24 fps, Progressive Main Profile. MPEG-4: 640 by 480, 30 fps,
H.264 which looks pretty damn amazing and is very compact, it just takes ages to encode. I play iTunes tv shows through my laptop onto my TV now and they look better than my digital cable so the codec is capable. Im sure there will be a differentiation between downloads for web and downloads for tv eventually. And once everyone gets next-gen broadband im sure it'll all go away...