Nothing to be suspicious about, that's just we are seeing, can't tell you if it's representative of what others are seeing (although the %'s seem to be in the right ballpark to what others have reported). Spikes seem to be related to when an update for one of our apps come out, e.g. around the 2nd (the big spike) is when our update to Discovr Music came out (https://itunes.apple.com/au/app/discovr-music-find-new-music...) I guess people who updated to that are more likely to of updated to iOS 6. In that actual release (2.6) we are seeing more like 75% iOS 6 usage.
Yeah, that would be interesting to also show what percentage of people are on the latest version of your software. A lot of less techie people just never update anything, unless it breaks.