I can explain since I know technically how it works.

You DL speed is dependent on 1: how fast other can upload to you, 2: if your upload isn't saturated, not used up. so capping is a good thing since putting it on unlimited will pretty much slow you dl to a crawl if all your upload is utilized. Its good to upload but not really neccessarily if there are T1 or Faster user, who can do it much faster then you alone by at least 10 times. so let them do the uploading, most of us are better off being a leecher and should not have to sit there and be a milker for others to leech, its too slow anyway.
Capping our upload to begin with is a serious handicap/hindrance to our download speed. their intention is to make it hard to share files with others and does just that, and worse because to download at full speed say 1.5mbit, at least 128k is used up. so someone with only 128k upload can spare nothing! doing so, slow their DL to at least half and thats a horrible tradeoff.