E3 is for unreleased games, mate.
It's about marketing and building anticipation, not to actually sell anything.
A lot of times studios set up booths and computers and allow people to play the beta even before the closed beta is sent out and they often handout beta keys and merchandise.
It's usually for the bigger, wealthier teams, but I remember hearing that Konstantin went to E3 or some other convention a while back for DoF, was wondering if he was going to this one.
Leipzig would be another good convention to go to. I believe the Lead Designer lives in Germany and they have a HUGE market for RTS games.