As mentioned above, not all programming on HD channels is HD either (there was mention of daytime vs Prime time programming), which is irrelevant, it's whether it's true HD or upconverted SD (standard definition), or perhaps WS (widescreen).
See the following post:
http://www.digitalhome.ca/forum/showthread.php?t=76068
The BTV IPG usually shows whether the programme in question is HD or not. This is not 100% accurate, but it is an indicator, while watching programming on an HD channel means nothing.
I believe that BTV HD STBs default to 480P, so, also as mentioned above, this should probably be changed to 720P (since BTV sends all signals as 720P.)