The difficulty may be that you are thinking of bittorrent as a client-server technology like a standard http download where each downloader must go to the same particular server to obtain the file.
Rather, each peer gets a list of other peers who are interested in this particular torrent, from the tracker or via DHT or Peer EXchange. Then those peers connect directly to other peers on that list, and the peers exchange pieces of the torrent directly with each other. (The transfer of the data is from “peer to peer”, which is what distinguishes this technology and why it’s called what it is.)
Most of the pieces that you download come from other leechers, not from seeders. All leechers download AND upload at the same time, and that is both required and self-enforcing. A leecher is, in effect, a trade partner. Each trade is a mutual decision, and bittorrent’s famous “greedy algorithm” leads it to seek out the best partner it can find. There’s more to that, of course.
A peer could obtain the entire torrent without ever having contacted a seeder. Every piece, he got from somebody else who got it from somebody else who got it from the original seeder. And he could, theoretically, get no two pieces from the same source.
I made and seeded some torrents, put them up on Demonoid and seeded them up to where there were three or four other seeders. That took about three days. Then I just stopped. Those torrents are still going strong three years later but I haven’t had anything more to do with them in all that time. They have a life of their own.
The peers find each other on the tracker or via DHT, but then it’s all individual transactions between peers. This is much like the way a good joke spreads, and there’s nothing to point back to whoever actually first thought of it.
When you’re logged in to iPredator, your dealings with the outside world have an IP return address for iPredator, and it forwards that traffic to you. But iPredator makes no record of this, so as soon as the transaction is complete, there’s no trace that it ever happened. Les flics can demand to know who was at the other end of IP such.and.such and iPredator can honestly answer, “I have no idea. There never was any record of that. If you’d asked me while the transaction was actually going on, maybe I could have helped you, but a microsecond later, I couldn’t anymore.”.
A server like download.com needs a fixed address so that it can be found. A bittorrent peer does not need a fixed address or even a DNS record. This is why you and all other peers can freely disconnect anytime, and reconnect whenver you like, using the tracker or DHT to re-find each other – but because there are enough peers, all of the time, the system keeps working just fine.
You should note that this scheme will only work on a network like the Internet, where there are bajillions of people with diverse interests, connecting 24x7, all over the globe.
Bittorrent doesn’t work at all on a private LAN with just a few people. It wasn’t designed for that. We already had enough protocols for that kind of situation and didn’t need another one.