Just because the returns are lower doesn't mean it's not viable. There are plenty of Android success stories. Even Angry Birds makes more money on Android than on iOS last I heard.
One of the big challenges on Android is Google doesn't have many credit cards for Apps so right there non-free apps are in trouble. Android may have double the iOS market share but if they only have half as many credit cards their effective market share for paid apps is 1/4 their true market share. That's before you even look at customer demographics, etc.