Random digital events aren't fun. You can't even go there and play the games for yourselves. Granted, most of us can't go to E3, but I will sure as hell visit gamescom in august. So I'll say yes, such events in general are a good thing.

E3 isn't just an event directed towards us, the core gamers. It is very much a press/media event. It is one of the only events where even the mainstream media is present to report on the biggest gaming news. Through E3 the developers and publishers are able to get their news across to the people who may not always be searching online for trailers, i.e. the mainstream audience.

So yes E3 is very necessary to reach a broader audience. Not to mention the hype it creates for games like Watch Dogs which go on to become million sellers. A simple online trailer can not generate that much hype which can only be produced when the media gets the chance to go hands on with the game and interviews with devs/pubs.