Interesting point. If it does, there is either something fishy with the statistics they reported or the vast majority of iPhone users are just upgrading yearly (and I doubt the latter is true).
Not really, there are just two types of OS adoption statistics and in this case Apple is using the same type that Google uses.
There are percentage running newest OS version of ALL devices with a certain OS or percentage running newest OS of devices that have recently accessed the appstore/play market.
Google is usually reporting the latter, percentages of devices that have accessed the Play store in the last month.
Of course those numbers are not perfect, as many users who have older models don't browse for new apps, so the iPhone 3G that is still running iOS 4.x is not counted, because the owner probably has all the apps he needs and there are no app updates for his apps anyway, because updates nowadays usually require higher iOS versions, that are not supported on the 3G.
So these numbers don't represent ALL iPhones, they just represent all that are still actively used to get new apps (or at least update apps).
BUT: This is even worse for Android than counting all existing devices - because it shows that 95% of actively used iPhones (iPads etc..) will be able to use iOS 6 APIs, while more than a third of all the actively used Android devices are still running Gingerbread.
That also sucks for security, smartphones are computers and you wouldn't use Windows 98 to surf the web or use onlinebanking nowadays, because it has no support for security updates anymore.