If you're making a mobile app, or especially something for tablets, in a lot of cases most of your users WILL be using Apple products even if it's not specific to iOS.
See this post on asymco:
http://www.asymco.com/2012/11/26/the-android-engagement-para...
And if you look only at the demographics you're interested in, it's likely that iOS will be at or near the top anyway.