Ultimately E3 is about promoting the gaming industry as a whole. Could the video game industry have benefited as a whole, if they parternered with Youtube? Youtube benefits by having viewers use the site, especially when they want to watch segments, and for forum posts when people embed videos on the forums. Game industry benefits by exposing all of their advertisements (pretty much what E3 is) to people who wouldn't have watched E3 (or know of it) anyway.
Edit: And I mean Youtube promotes E3 videos, has it on the very front page, and has E3 themed backgrounds, words, etc.









