I am pro Android at the moment, and expect to stay that way (my bias disclaimer). But I too don't want such a dominant player. Then again, such is the nature of open source with its neverending ROM's, developers and many manufacturers, that it will always drive innovation? Perhaps it does not matter being overly dominant. But I still hope iPhone innovates at a greater pace.
I wish they could analyse that 72%, and readjust it for just high end smartphones (or what was considered as such for the last 2 years, the ave length of a contract upgrade). Of course, iPhones older than 2 years will also be excluded. Maybe the Android dominance figure will be lowered, but I reckon it will still be far ahead. And with this analysis, the 'apples compared with apples' argument will be satisfied.
As to why iPhone users spend more: has it ever been considered that they spend too much? We know a large chunk of iPhone buyers are influenced by the 'glam', 'exclusivity' and 'image' factor that iPhones presumably provide. Those are the people that will mind less to pay more for apps and stuff on the internet. Android users, the ones that knew what kind of phone they are getting and researched it well (most people who research an upcoming phone choice well will opt for Android in my opinion. Or they should, but lets not let the argument devolve around this) are savvy users, and very picky about what they buy on the app stores and the internet. Rich Apple users are less so discerning, in my opinion.
Of course, apps tend to be cheaper or free on Android. That's a factor, too (with regards to difference in spending).
That 72% Android figure is a worldwide figure, is it not? It is closer to half-half in the US, (I think Apple held a slight edge in 3rd quarter sales there due to iPhone 5), and internet buying is much more established in the US than elsewhere. This could help explain why 'iPhone users spend more'.
Given the above, I think it would be incredibly stupid for developers to look at Android after looking at iPhone, at this stage of the race.
In my opinion.