Leaks come from people within the E3 event, usually during stage rehearsals and such, which won't occur until later. Leaks don't just materialize out of thin air, there has to be people in the know leaking this stuff when it starts getting discussed more openly, and that's going to happen about a week to a few days in advance of E3.
As a side note, never understood why people hate leaks. You're learning new info regardless of when it is, I don't see how it's spoiled other than there's less fanfare surrounding a leak then an actual showroom reveal. But either way, you get new info, you get hype, you move on. I'm not going to say no to a handy just because I wanted a suck.