but it does result in loss of detail.
It varies by channel, they definitely don't all use the same bandwidth.
Absolutely. My 'main' TV system is setup around an open-source PVR (mythtv), that simply records the broadcast transport stream bit-by-bit, which means the recorded file sizes are indicative of the bit rate.
File sizes vary of course, but an hour of BBC1 typically produces a file that's a bit over 2GB. An hour of film 4, usually well under 1GB. One artefact of Film 4's low bit rate, that I find very noticeable, is a pixelation that occurs when a scene makes a transition whereby detail emerges out of a dark scene. Same is noticeable when if the producer choses to slowly fade in the credits over a black screen, in which case the text often appears momentarily pixelated until it reaches full brightness. I've only seen that on the low bitrates, like Film 4.
As another aside, I've recently enhanced my system with a blu-ray player, and wow - now that's a good picture, and justifies the whole large-screen revolution for me. Best I've bought so far is BBC Planet Earth, which I probably under-appreciated when first broadcast, but in full HD it's absolutely mesmerising.
Blu Ray makes me want a bigger telly though, mine's 'only' 40 inch, and I'm really struggling to get purchase approval for a new one. I will try HP's argument about screen size being half the viewing distance but I suspect I'll just get reminded how new the existing one is, and how much it cost.