Knowing Apple, they probably won't make a mistake again like the iPhone 4 with its antenna issues. But then again, iPhone 4 sold a heck of a lot regardless. I say this could go either way.
They won't make the same mistake again in the next model?
They never fixed the crumbling MacBook palm rest problem until the major redesign, or the MBA hinge problem, or the iPhone 3G/3Gs case cracking at the corners, or the overheating of the MBA. Never until the next big case design.
It's not even certain that they fixed the iPhone 4 antenna issues since the successor isn't out yet. The Verizon one obviously needed a different antenna because it operates at different frequencies (antenna length and design is highly dependent on frequency) but it doesn't say anything about the next GSM model.