Don't know about E3, but GDC badges are RFID tagged ones, which is why it's a quick swipe and go for verification. IIRC, people have brought up the idea of RFID tags to those guys at the Q&A sessions, with someone who's actually did that kind of badge security stuff. Not sure if they ended up going with them. I guess it'll happen when they DO run into trouble of overcrowding, and when it finally cost them money to have to turn people away.
The problem with picking up the badge the day of the event is that you really can't have a line of 40,000 people on Friday morning just to get in. Sadly, the bulk of their operation relies on volunteers at entrances and such, so constant checks are most likely out of the question too.