Google I/O got sold out because every body who got the ticket knew that they are going to get a latest android phone which is priced higher than the ticket price! Definitely a big motivational incentive to hit the buy button.
Not true for all attendees but probably for a good percentage.
To say that attendees know they will be getting the latest Android phone is a little presumptuous. That'd be like saying if I wanted a new car, all I need to do is be an audience member on Oprah.
Not true for all attendees but probably for a good percentage.