Sure, many use BitTorrent for piracy, but FTP, the most used protocol to transfer files(to/from webservers, home users, companys, etc), is also widely used for piracy, just not as much in public, and you don't see anyone trying to stop it's use.
BitTorrent is a good way to distribute larger files to many users without putting strain on single servers and connections.
By using it more and more for legal purposes, it could loose some of it's "piracy-tag".
And by the way, if people wan't to download the game illegally, they already know how to use BitTorrent or any other necessary protocol.