I'm more than willing to believe Android users on average buy less apps than iOS users. But that just means different business models will succeed there.
A subscription based model is more demanding to maintain, vs a pay-once-app. You at least don't need a server to maintain subscriptions. Ditto with In app purchases (which also require you to maintain a server to keep track of who has paid for what).
If you're looking to reach users of your non-app-centric service that you're looking to provide a free app for, targetting Android is a no-brainer if your service is aimed at demographic groups in which Android has sizeable or even plurality user adoption. That's most of them, but not all.
Looking through apps on my devices (I'm one of the "cheap" Android users with zero paid apps), Flickr, Evernote, Mint.com, Opera, car2go, Skype, Starbucks, Kobo all stand out as quality apps that pay off for the developers in other ways.