When they sue you, isn't it actually for the uploading (the "posting" of copyrighted material by allowing other torrent users to download bits of the file from your computer) and not the actual downloading?
Is that why they don't target DDL users of sites like Rapidshare and Hotfile, because the file is only downloaded but not uploaded by the user, unlike on torrents? I'm sure trying to seize the user logs of DDL sites through some form of legal action might be difficult as well.