When Hardy Heron was released, the Ubuntu servers became overloaded with thousands of people trying to download it. Downloading rates of repositories and updates were so slow that some people had to leave the computer on at night only to find connection errors the next morning.
We do actually have a BitTorrent tracker and support BitTorrent downloads; you can see the .torrent files on releases.ubuntu.com, and every release features people eager to provide seeding.
I think the reason the torrents aren't prominent on getubuntu/download is that there are a lot of problems with the server-side tracker software; particularly around release time, it has to be restarted manually rather a lot as new files are made available, taking ages to reinitialise each time, and this makes our sysadmins unhappy. Our webmaster also wants the download page to be as simple as possible, and each option does add a level of complexity to the process.
That said, BitTorrent certainly can help to scale back server load (although so can using mirrors other than Canonical's - there's a reason there's a period before release when the images are available on our servers but we ask people to restrain themselves from posting links to them, and that's to give mirrors a chance to fetch the images first).
On 3 June, our webmaster added a note to the bottom of http://www.ubuntu.com/getubuntu/download on how to retrieve images by BitTorrent, which I believe was in response to this item. This ultimately takes you through to the releases.ubuntu.com page from which you can get the .torrent files.
Bearing in mind some of the constraints involved that lead to something of a compromise, I'm interested in whether that resolves this item.