You can always start your own chain, you can tell this by how many coins there are right now. Litecoins, bitcoins, terracoins, namecoins, the list goes on. So, yes, you can have your own version for your own purposes, it doesn't effect other chains.
torrents are just a great way to distribute data, it lessens the load on the official ubuntu servers and lets everyone pitch in to distribute the file.
World of Warcraft's updater apparently also uses torrents to update the game of clients. It's a smart move, I'm not sure if the updater also...