well over 90% of people who have the copy on Doom3 earlie obviously did not get it in a shop or through the post.
and if you look at the threads with the people who allready said how cool the game was sunday and monday (the leak was saturday) you can easily count on different forums how many people downloaded it.
ID could have managed to but up their own bit torrent tracker where you could log on after you paid through lets say paypal and then people could have downloaded it. through email you get a key to activate your copy which also needs to be registered online before you play otherwise the game is locked due to a hacked exe or something.
not that hard to implement.
they could have also released a demo 10 days ago! that would have easily stoped 30% of illigal downloads cause loads of people are realising the game is just another FPS and would not have bothered downloading 3 cd's.
50.000 they gonna sue. Thats a lot of people. Wonder if thats again just the USA and germany. (it will be US only)
p2p is to easy to many people do it. not everybody gets caught.
get rid of IRC and bittorrent tracker websites and we would have over 50% less piracy of this game. any many many other p2p things.