I was guessing, but looking it up ... Gartner are talking over 200 million tablets per year, of which only 50 or 60 are iPads (according to the Quartz charts), so I'd say it's in the ballpark. (I'd expect the Androids to decay faster, though ;-)
http://www.gartner.com/newsroom/id/2954317
"""
Device Type 2014 2015 2016
[...]
Tablets 216 233 259
"""
How so? Android and Windows tablets never sold as much as iPads and still don't. It might be 50-50 now, but not 3 times as much by any means.