Yeah... This is going to be the focus of the events. The significant hardware internal upgrades will be a part of it, but the overall package will be mainly focused on the software side.
It is pretty clear to see. The more I consider all this, I see no chance that two different unique iPhones are announced on Tuesday. There is no way Apple would do that. There is not enough differentation for them to exist at this point, so it is not going to happen. We will have a 4S device, which allows Apple to have superior production because the externals are essentially the same, and they can support the device with the software.
The software is what makes the phone useful anyways, so I think people who say that they will only buy a phone that has a redesigned exterior and do not care what the software changes or hardware changes are, should just be ignored. They seem to be off their hobby horses at this point.
iOS and hardware more important then external design. Especially when you have the foundation of when of the best designed consumer devices in the history of mankind.