I think I wil reevaluate my decision to purchase after sept 30, too.
Then you're delaying for no reason, except one that you've manufactured in your head. If it bothers you, get something else.
Think about it: there's a class action suit out there about the antenna issue. If Apple planned to "fix" the problem by September 30, do you really think they would get away with saying "hey screw you guys who bought it first, only new ones get the fix."
The ship has sailed. Anyone who actually listened to the press conference, and has read about the press tours, should come away with the conclusion that Apple's top brass believes they did everything they could've done with the iPhone 4, and aren't about to mess with the design any further. At best they'll tweak it for next year's design when the next iteration comes out.
At the end of the day, the only test that matters is the one you do, holding it in your hand, where you live and work and spend time, making and receiving calls. You get 30 days to do that. If you're unwilling to do that, then don't buy it.
The only thing that's likely to change on September 30 is Apple's policy on distributing bumpers. I predict by then the only manufacturing or design change is in the boxes iPhone 4s ship in: they'll be slightly bigger to accommodate an included bumper.