[objclxt]

I can collaborate that data somewhat - across the US apps I have access to stats for (a sizeable number of users) I see a similar figure (~6.5%) running iOS 4.3 and lower.

However, only 0.7% of devices are iPhone 3G and lower, so the majority of users I see running <4.3 are not updating out of choice.

This is all anecdotal, though - figures will vary dramatically across apps/demographics/etc.