[Mac-the-T]

I reckon there is a difference. I can tell watching football on on my father-in-law's LCD - he has Sky HD.
In HD you don't get much benefit while the game is moving fast and the camera is way up for a wide angle view. But when the action slows, for a corner or throw-in you can see so much detail. Advertising hoardings and faces in the crowd, many rows back, can be seen in far more detail that normal TV - you can recognise faces.
Another difference can be seen when viewing digial photos on a TV.
PLug a computer in to a VGA or S-video port or other standard connectino and you get pretty blurry, grainy photos on the TV.
Plug my laptop in via HDMI and I get full screen, lovely sharp photos.