I think the problem is that when Apple decided to wait a little longer, everyone assumed they needed time because they were working on something big. If they had presented us with the 4s in July, I don't think people would have been nearly as disappointed. By waiting until October, they blew expectations up much higher.
While this is probably true, you have to think that Apple had a bit of a fiasco of a launch on its hands last summer with the release of the iPhone 4. It launched in very few countries and even where it did get released, it took several months to build up stock. I had to line up at an Apple store for the better part of a full day late September last year to finally get one.
I would imagine they waited for three reasons.
1. To build up stock on the 4S so it would be more widely available at launch time.
2. To make it coincide with the release of iOS 5 because some of the iPhone 4S features depend on it.
3. To break with their product launch cycle, so the competition doesn't know precisely when the next new iPhone will be announced.
I would not be surprised to see an iPhone 5 announcement in the next 8-9 months. There are obviously prototypes of it floating around at Apple headquarters. However, the fact that they did not release it could be due to external factors.
For example, what if they were anticipating that certain components would drop in price since they started designing it but that has not occurred. Or that manufacturing process on the new body of the phone would get streamlined and it hasn't?
They must have known that the tech world would be underwhelmed by this annoucement, but it's not like they're going to tell us what really happened...