Not true, games distributed on Steam are still pirated. There were hacks to give you every Steam game on your account, and hacks to make pirated games work online. I'm not sure if they're still around. Anyways there are most likely at least hacks to uncouple Steam games from Steam and allow for offline and LAN play.
However Valve is betting you'll find Steam more convenient and having more features than pirating: download and play your games anywhere there is internet access, integrated server browser, community features, Steam Cloud (coming any day now...). With traditional games pirated games are more convenient (no need to have the CD/DVD inserted while playing, can download the game from the internet instead of having to have it shipped or go to the store to buy it).
For some of the first third party games such as Defcon this was true, but Valve released an SDK or something with source code for a stub to tie a game to Steam easily... all my games have been updated, except of course the iD ones that use DOSBox.