Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Its simple. Apple had no clue of the official launch date in time for ATT to give proper notice to its employees. Apple just said this is our target range and came up with the official date... moments before the keynote :) Notice the commercial didn't have a date either.

Ah, the joys of corporate software / hardware development
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.