Please bare with my spelling - I'm on my phone
Before I go on, the 's' in 3Gs stands for speed - it was in the keynote.
What I think happened is the iPhone 3g was rushed out last year to fill the spot for the iPhone 3Gs because it wasn't ready yet. So in reality the iPhone 3Gs is the real iPhone 3G. I feel that next years iPhone (what ever it may be called) will be the iPhone that was supposed to be released this year.
The only hardware that was increased (significantly) was the addition of a compass, upgraded 3MP camera wit video recording capability and (correct me if I'm wrong) double the ram. The compass (to me atleast) wasn't such a big bonus, but the ram was.
If you have a think about it, voice control, video recording (my 3g can record video via cycorder) and other features the 3gs has, all the other iPhones can have. So why did apple not let us have this stuff? To make the 3gs seem to hAve a bigger upgrade.
Here in Australia I can get the new 32gb 3gs for $0 and then extend another 2 year contract but I'm not going to because I feel that next years iPhone will be focusing more on hardware rather than the software, although there will be some minor tweaks obviously.
Just my 2 cents on what's going to happen.