You shouldn't be looking at it like that. You should be looking at how many people have 3GS and first-year iPhone 4s, who will be either 75% through their 3 year contracts, or fully through them, when the iPhone 5 is released. That number of people is enormous, and the vast majority of them have been waiting for this upgrade.
To be nobody but yourself - in a world which is doing its best, night and day, to make you everybody else - means to fight the hardest battle which any human being can fight; and never stop fighting. -- E. E. Cummings