There are quite a few companies that provide insight into browser (web) usage statistics. Both StatCounter and NetMarketShare provide reports that you can just point your browser to. Chitika provides detailed analysis of topics-of-interest.
One criticism of these data when applied to mobile platform analysis is that they do not include app usage. Hence data usage from the native Facebook, Twitter or WhatsApp applications are not included. With PCs, most people use web browsers to access online resources so this is not an issue. However on mobile, we know that a lot, if not most of Internet access is actually through these native applications and not through browsers. Therefore the data from StatCounter, NetMarketShare and Chitika is less relevant for understanding user behavior.
Data usage on carrier networks is separate statistic that provides information from a different angle. This counts traffic from both native applications and web browsers. However it only includes usage on the carrier networks and does not include WiFi usage. Let’s compare this data.
First web usage data from StatCounter for Europe, Oct 2013 (only mobile data excluding tablets). This data shows that Android is a little bit ahead of iOS in web usage. Compared to the US, Android usage is higher in Europe. A common explanation is the lack of attractive subsidies for the iPhone in Europe, which make the iPhone much more expensive to own than an Android phone.
Asymco recently tweeted data usage on network carriers in Europe for the same period (source Amdocs). We immediately notice that iOS (iPhone) usage is much higher compared to web usage.
These two sets of data are not directly comparable, and care should be taken in their interpretation. Regardless, considering other evidence, I think it is safe to say that iPhone users seem to use Apps much more than Android users. This is why Android beat iPhone in web usage, but lost in total data usage.
This is unlikely to be a simple App ecosystem issue. Although developers still tend to target iOS first and Android second, for the apps that most people use, these are already available cross platform. These cross-platform apps (Facebook, WhatsApp) probably constitute the vast majority of data usage and it is difficult to image that iOS only apps make a huge difference.
I don’t know the answer to this. You could say that it has something to do with engagement, but it’s a pretty broad term and I’ve never seen information that tells me how user behaviors change with engagement levels.