Are iPhone owners more willing to pay for applications than Android owners? Or are Android developers just more interested in giving away their apps?
Why the disparity? Pingdom speculates that maybe more Google developers are just hobbyists or tinkers who can get their app in store because they don't have to deal with Apple's gate keepers. Another important factor, Google only supports paid apps in 13 countries.
It's also much easier to install pirated software on Android phones than it is Apple phones. So perhaps this pushes down sales.
Maybe it's just cultural? Google gives away Android. Apple does not.