I have a very crappy 99$ android phone[1] with gingerbread, a Nexus S, a Nexus 4 and a Nexus 7. Everything is tested on all the devices to make sure it works. I think that with this devices I can catch pretty much all cases, from low end to high and tablets.
my principal app is an Imgur(image hosting) Gallery viewer so I'd say mostly young people that do a good usage of social networks & media so people that usually "keep up with the technology".
In fact my usage statistics are the following:
Android 4.0.3 - 4.0.4
29.55%
Android 4.1
28.99%
Android 2.3.3 - 2.3.7
28.37%
while for the rest of the app in the entertainment category the is the following:
Android 4.0.3 - 4.0.4
29.76%
Android 4.1
15.31%
Android 2.3.3 - 2.3.7
40.07%
you can really see a difference but 2.x is still quite strong everywhere so it's usually worth to have some kind of support, even if the app doesn't run greatly users will generally acknowledge that they have a crappy device and not complain, for instance I' d say that 100% of support requests are from users with high end devices.
[1] http://www.huaweidevice.com/resource/mini/201008174756/ideos...