Because honestly, any company with a warchest like Apple's can afford real marketing. Who is this supposed to be targeted at anyway? The readers of Gizmodo and pcmag? Last time I checked, those arent even close to Apple's core market.
The general population just kept living their lives. What got people actually talking was the actual launch and the TV spots.
Now why would you let the cat out of the bag early just to whet the appetite of a small group of hardcore geeks?
Because you have everything to gain and nothing to lose?
I think you underestimate the noise geeks make. I'm sure it will be reported by mainstream media. A fitting headline would be:
New iPhone scheduled to be released in October lost at a local restaurant!