Bittorrent ratio practice possibly very faulty

I was looking over the specs for the bittorrent protocol and I can't help but wonder whether those sites which use upload/download ratios are in fact using a very exploitable system, since bittorrent trusts the client to report the amount of uploaded bytes.
Perhaps a telneting to the tracker with a simple HTTP GET request is all it takes, but I would like your opinions on this and how it would be possible to do this under various OSes, just for the love of computer science and all that