I thought I'd share some figures that are a bit different for several reasons.
I only have figures for my free app ShootStorm Survival. The figures come via Mobclix who I use to provide the adverts. Both the free app and advert only statistics may make a difference.
In the past 24 hours, 48.3% of users have iOS 5.1, considerably less than the developer in the original post. 22.4% are on 5.0.1.
What is interesting is that the latest version of my app only came out 4 days ago, but 67.2% of players are using it. So they are updating the app much faster than the OS.
25.4% are on 3.1.2, the previous version of the game. So over 90% are on a recent version.
Part of the difference may be due to my app still working on all devices. So there are players restricted to 4.2.1 (5% of users are on that version) or 3.1.3 (unknown amount as it falls into the Other category) (Other refers to the total outside the top 5 iOS versions in use and is 8.5%).
Also relevant is that 75.1% of users are on iPad, and 79.1% on WiFi.
EDIT: I should note that these figures are based on an app that is well over a year old, and has relatively few players, so may not have the statistical accuracy of the original story.