Take it from a CCNA as well as CCNP... This *IS* how congestion works. -everything- will deteriorate under congestion.
If you really want to become technical... Whether it's a HTTP download, or a youtube video, the packets will still be broken up to 1500 bytes. It doesn't matter WHAT data is in the packet, a packet, is a packet, and ANY packet will get dropped when there is congestion. Anything you download that is bigger than 1500 bytes, will, and can, potentially be dropped under congestion.
You are shaping - the HTTP download test done over multiple ports as posted by a previous user proves this beyond doubt, seeing that you CANT argue with it, you simply just pull up your shoulders and all of a sudden claim you are no expert?
If you're no expert, then please don't come and try to explain how congestion works. You obviously don't know how that works either.
YOU ARE SHAPING. Finish and klaar. I think we should all be lodging complaints at the ASA and ISPA right about now...