That would make too much sense....
Seriously, just for the peace of mind for users of the product, just come out and say, we're releasing the update on Friday, Sept 28th, sometime late in the afternoon. Period. Done. People can stop crashing their servers from checking for updates every 5 mintues.
Maybe they simply dont know? You have no idea the status of the release. What bugs or features they may be working on. It could be many things. Like stated above, if they released a date, and then had to backpeddle the PR would be much worse than had they just saying nothing or said its coming "later".
Remember, only people here and a few other sites are even aware a update is even coming, a good majority of the iphone userbase is simply unaware of the pending update and are out ENJOYING their phone and not stressing day after day for a end-all feature update.