I think I see E3 as simply a celebration of our hobby. Obviously, the money could be spent on R&D instead. We could also stop spending money on games altogether and become monks and nuns. But since we don't, why can't these hard-working programmers take a few days off to just get excited about games, theirs and everyone else's?
We did the no-E3 thing. Everyone hated it. And while you feel like the independent games get drowned in the mess, consider the alternative: no E3, no exposure whatsoever, and press gala events reserved only for the EAs and Activisions of the world. (This is what happened when E3 wasn't around).
The press likes to groan about E3 because, I think, they have to be super busy for a week and it all seems silly when you're up at 3am writing a preview for the latest Wii crap. As for why non-press hate a period of free celebration (for them), I can only imagine.