Featured torrents on most of the more popular reputable public trackers will promote legal torrents, unlike the questionable ones uploaded by most users.
Mostly small unknown bands and developers of freeware/donationware that the admins of the site feel needs a little attention. I know Demonoid often features various bands who intend for their music to be free, often with a Creative Commons license, too.
In addition to exposure, they get feedback in the form of torrent comments by those that do bother to download it and try it.
Torrent trackers like to put stuff like this on the front page to give the impression that they are a legal-minded site and to dispel the popular notion that all torrents are copyright infringing illegal materials and that there is no legal use for the technology.
Incidentally, the very first place that one could obtain my software, before I had a website of my own, was through P2P. I was sharing my stuff on WinMX, just like the other developers that inhabited my programming chat room.
It was cheaper for me to do this than to pay for a domain name and hosting. Plus, since most people that downloaded it also visited my chat room, I was able to get instant feedback, comments, suggestions, and bug reports, and they were able to get support much easier.
In many ways, my chat room was very much like DonationCoder's community, only it was located on a P2P network instead of a website.