Yeah, there is a big difference between iTunes HD and BluRay HD. I'm showing around 4.4mbit for the 1280x720 HD version of Warehouse 13 I got from iTunes using H.264. Avatar off BluRay is 1920x1080 and runs VBR, with it maxing out around 40mbit, and usually averaging somewhere in the high 20s to mid 30s, also using H.264. I can easily spot some compression artifacts and blocking in the iTunes video when played back full screen (2560x1440), but nothing really stands out when watching Avatar. If a digital copy came in HD for Avatar, it would at most have around 7mbit to work with to also still fit on a dual layer DVD.

This is why I could care less about most streaming services for HD right now when I want a full cinematic experience at home. Sure, the Roku and others can output at 1080p, but I highly doubt any of them actually deliver a good enough bitrate to come close to BluRay quality. Hopefully faster broadband options start rolling out over the next few years to allow the streaming services to improve quality. It's pretty good now, but could be great once they stop worrying about people on sub 10mbit lines.