I think it's probably more because they know that the 4S is going to overshadow the announcement. Despite what the tech blogs and the armchair analysts want you to believe, the 4S is going to be huge. It's going to sell like hotcakes. This is not going to be like the Verizon iPhone 4 launch--it's an actual new model.
2 examples of media vs. the real world:
1. Riding the train home last night, I heard a group of people talking about how they can't wait for midnight to pre-order the new iPhone. Rather than talking about how disappointed they are that it's not a new redesign, they were talking about all the huge upgrades it has over the 4, most of all the Siri integration and the camera. People are excited about this phone.
2. My wife is a teacher at a middle school. She is surrounded by Apple stuff all the time. Her students all have iPods. It's an Apple-centric school, so they grew up on Macs. They are now thinking of deploying iPads in some classrooms. Yet, none of the kids really knew who Steve Jobs was when all the news was breaking about his death. They vaguely seemed to know he had something to do with Apple, but that's about it. It's really sad for all of us who grew up watching him innovate, and out generation appreciates that the iPhones, Macs, and iPads we're using were all his doing. But the current generation of up and coming users do not attribute him as much to Apple as we do.
The big story here is that the tech media adds a lot of BS to a pretty cut and dried situation: The iPhone 4S IS a new iPhone model, people ARE excited to buy it, and every other smartphone maker knows that this is a bad time to launch a new handset. They will wait for the hype to die down, and then launch. And by then, the next Android Best Phone Available of the month will have already come out.