Most programs are written for business cases other than getting money from license sales to individuals.
Last year I wrote an Android app for a gambling company that now generates 4.5 million Euro in revenue every single month. And the app is not even in the Play store, you have to download it from a website that is embarrassingly hard to find. And the app can only be used in countries where gamling is legal.
We did not charge 99 cents for the app, and somehow there was money to pay my bills anyway.
Then there is the ebanking app I used today: free. And the hipmunk app I use to search for flights. Free. And the audible app. And the kindle app. And the facebook app. And the ebay app. And the Google Search app. And the wikipedia app. And an information app from my government. And the app that let's me see the TV program.
All free of charge. Still, there is a business model and good money behind almost all of these apps.
Again: there are definitely certain apps that you can sell for money, and statistics about how many people buy apps on each platform are of course interesting.
But app sales are not what makes a platform live or die. What makes a platform live or die is reach.
Android is currently in the hands of most people that own a smartohone. That includes rich people and poor people and those who buy apps and those who don't. If you want to reach people through their smartphones, then you want to make an app that runs on Android.
If you think about it, that's how FTP or Poker Stars works. Download a free client, even play for free for play money, earn money on rake once they convert to 'real money' players.
If Android becomes the platform that "everyone" has, then the next disruptive consumer change is, almost by definition, going to happen there. This is largely what happened to the Mac -- the platform that had the best of everything in 1988 was, by 1994, suddenly unable to run all the new toys everyone wanted. When Win95 was released it wasn't even all that technically superior anymore. And by 1998 it was almost dead (and, but for the iPod's success, probably would have died).
[1] https://play.google.com/store/apps/details?id=com.facebook.k....
Regarding your second link specifically I know lots of folks who stick to using LTE on their Android devices instead of their wifi because LTE is often faster than their home internet, so I'm not sure that showing Android phones are less likely to use WiFi really means anything.
Actually Akamai research confirmed that Android and iPhone are neck to neck for cellular traffic. Because of the iPad wifi traffic for iOS is more than Android but that may change with the release of Nexus 7.
The direction does matter and android web traffic is definitely where I can see it.