Android 3.x was "the tablet OS" which was not very suitable for phones. The problem was, Android tablets back then (Motorola Xoom et al) did not exactly set the world on fire.
Almost all the phones skipped 3.x completely and moved from 2.3 to 4.x.
Actually, I thought it was interesting how different they were, at least in some respects. If you look at the ratio of pre 4.0 versions vs post 4.0 versions, in the Unity stats it's about 27% vs 72%, but on the Android dashboard it's 45% vs 54%.
Perhaps Unity apps aren't as widely used on older devices and thus the stats are skewed in favour of more recent versions of Android.
Then again, the Android dashboard data is collected from the Google Play Store, so it isn't a perfect representation of all Android users either.
Yeah could be just different demographics (and as usual, with any data set you have to keep in mind that it's not "perfect").
E.g. Unity apps are mostly games, so this probably represents "android users who play games". Whereas google's is "anyone who went to the store" (which I guess is a much wider population - as soon as anyone wants a Facebook app they have to go to the store, right?).
Android 3.x (Honey Comb) was just for tablets. At that time Android tablets weren’t very common, they become more popular after Android 4.0 was released.
