@Lee Dowling "iPhone users are more likely to have more disposable income from the start"
I think that that does have a great deal to do with it. It would certainly have a considerable effect on the figures in the US. Last time I saw any relevant figures some 50% of Apple's customer base in the US were males in the 20 - 35 demographic living in households with a combined income of in excess of $100k annually. Given the costs involved contra income with regard to mobile broadband it is unsurprising that iOS customers with well above average disposable income (although I am not suggesting that they are "1-percenters" :P) spend more time on the web than the average Android customer. We see after all the exactly the same pattern reflected in average spend on apps per annum amongst the two groups.