To put it another way, if they didn't do this release at all and just continued to sell iPhones with iOS 4.x on it for the next 12 months, I don't think we'd see a difference in their sales numbers.
I think this is a testament to the current quality of their devices and OS. But it does feel like we've entered Mac circa 1991. It's getting long in the tooth and the improvements are really small, while a competitor with a late start is showing signs of accelerating.