@vesuvius: Of the above mentioned, Google likely makes the least amount of money from app sales. And yet, they have the crappiest mobile web browsing experience.
There might be serious revenue in the retail sale of apps, but there is still money to be made by making LOB software. As the desktop is replaced by the phone, companies are going to be pushing their employees towards phones with a better browser experience, so they can deploy web based applications quicker.
It's difficult to do A/B testing on hundreds of features with apps, but on the web it is possible.