From the Apple SG site, it seems to me that only the first batch of iP 4 are affected by the antenna issue. Looks like those batches after Sept 30 will be resolved.
It looks to me that Apple is doing something to the phone internally to resolve the reception issue. Of course, they will not admit if asked, but looking at that line that says "To qualify for this program, you must purchase your iPhone 4 by September 30, 2010.", they are confident that their current stock will be depleted by 30 September, and new stocks with the correction (made internally) will not have this problem, thus it will be stupid of them to issue phone cases then.
Also, they rather issue out a bumper/case than recall their current stock, as this will help them reduce their cost, as they know from the initial release, a lot of Apple 'followers' will sure line up and buy their product no matter what defects it has.
So will you still buy?