It should be noted that the 8gb iPhone 3GS was not available at launch. It was added to the lineup as the budget option only after the iPhone 4 was released [1]. So this should not be a real surprise.

The real question is what Apple will do with the 3GS. Will Apple keep it available and turn it into a low-cost prepaid phone? Apple's own Tim Cook has suggested Apple is exploring its options.

[1] http://en.wikipedia.org/wiki/IPhone_3GS#Timeline_of_iPhone_m...

[2] http://www.bgr.com/2011/08/05/low-cost-iphone-could-launch-s...