Historically Android tablets have had support dropped much more quickly than iPads. I'm sure there are lots more Gingerbread, Honeycomb and Ice Cream Sandwich based tablets just sitting in a drawer somewhere replaced by shinier newer tablets running Jelly Bean than there are iPads which have a much higher "hand-me-down" or resell value even if the original owners move on to something newer.
Anecdotal:
I know a few people just now considering upgrading from their iPad gen 1, and not a single person who is still using a first gen Android tablet.
FULL DISCLOSURE: I work for Apple.
The other important factor for HNers is rate and volume of app purchases, the last figures I saw there were also completely dominated by ios - that is to say, Apple users buy tons of apps compared to Android.
Would be interesting to see the current stats.
There's probably enough external data to confirm that the iPad owns the real lion's share though.
E.g. http://gigaom.com/2013/07/23/the-ipad-accounted-for-84-3-per...