Like I posted earlier, it seems QoS is applied to http flows once they hit a certain size. (I'm guessing around 5MB based on my speedtest observations). So downloading a 700MB iso IS going to be affected. What line do you have?
It also appears that ALL your high-traffic flows go into the same QoS bucket - so your total speed for ALL down-rated transfers will be x kbps (512 on my line) in total.
Hmmm. I am on a 2 meg line and tried to download a +-1MB file. It still ran at 15KB/s.
Although a much larger file did go slower at about 7KB/s. So you may be right.