Your definition of what constitutes a first generation product differs from mine.
I could argue that you bought a rev a product of the iphone 3gs as it introduced a new cpu, and graphics among other things
An example of what I consititute a rev a product is akin to say the first core2duo mb. The next iteration still using the c2d chip with same platform would be a rev b. When they change the chip set, that would constitute a new rev product
Here is how I classify the iphone in terms of revisions
iphone:rev a
iphone 3g: rev b
iphone 3gs: rev a again
iphone 4: ?
The difference is that the 3GS isn't exactly new. The problems that arose with the initial release have been sorted out. I'm not having the same issues that the initial adopters did, because Apple fixed those issues awhile ago.
Note that I don't necessarily care about revision classification...its the flawless user experience that I'm after. When iPhone 4 is released (whenever that will be), its almost a given that its going to have some type of issue that will have people in an uproar...it happens every year with whatever product Apple revamps...doesn't matter what revision it is, it still happens. I don't want to play a part in that, which is why I wait.