Expenses aren't really a problem, and using torrents would be just another thing users would be forced to use.
Besides, we want to track downloads, and to track them using our current system (Google Analytics) we require users to open the download page and click the link since hot linking is prevented. Due to the release spike and direct linking to mirrors 343605 downloads were unaccounted.
Well okay, when I said expenses aren't a problem, I disregarded the fact that we used Amazon S3 for the release. Reliable, but incredibly expensive. Yeah, it would be a lot cheaper to ask for free mirroring, but organising file distribution 15 or so minutes from release when Mari0 was packaged would be a bit of a pain. S3 was an emergency solution when I realized at what rate the traffic was growing.