Last week I spent some time playing around with various BitTorrent networks. My initial download speed was very poor, ~20 KB/sec. After hand optimizing the various parameters in a BitTorrent client I was able to achieve an average transfer rate in the order of 65 KB/Sec - respectful, but still not great. My various downloads were taking over 10 hours to complete.
Today I am downloading Windows Vista build 5536 (Pre-RC1, 2643 MB) through Microsoft's official download site - my average transfer rate is 650 KB/Sec, a full 10x increase over my best BitTorrent average speed. On iTunes, I am also able to achieve ~650 KB/sec downloading TV shows.
The key difference here, of course, is that a company using BitTorrent to distribute a file is not paying much for the data bandwidth, while both Microsoft and Apple, in the example above, are incurring huge bandwidth costs. You get what you pay for.