Or this: http://techcrunch.com/2012/10/05/after-early-boom-new-number...
If they don't care, that's fine. They'll start to care as more things go iOS6 only. Just like people stay on XP forever until there's a reason to upgrade.
But 60% of the user base (including those who can't update like iPad 1, not just 60% of eligible) in less than a month? As a dev that make me really really happy and not scoff at considering going iOS6 only.
The combination of the iPad, iPad mini, iPhone 5, and new iPod touch all running iOS 6 and the aggressive older device update strategy means we are pretty much assured 90% by the end of this year, if not sooner. With the notable exception of the original iPad, the iOS devices that can't run/won't run iOS 6 are a drop in the bucket.
The other thing to note is that as devices get older, users tend to enjoy them less and therefore screw around on them less. This naturally results in less app usage, less browser usage, appearing in less statistics, etc...
So while the exact percentage of all iOS devices running iOS 6 might take longer than a year to hit 90%, I suspect app developers will have a fairly different picture painted for them by their personal usage statistics.