But what is their lifespan in use? Based on secondhand values I suspect the effective lifespan of the iOS devices is greater and therefore the share in market is greater than the share of sales.

Android is probably the more numerous still but the gap is probably much closer than the sales suggest.

2nd hand sales values do appear to be higher for iOS devices. And in my mind they are usually better built. So I agree the average lifespan may be longer.

But this doesn't mean that good 2nd hand Android devices don't get passed on to family or friends. All the devices in my family whether iOS or Android get passed along. The Android handsets are perfectly fine.