The one word answer is marketing.
This will open the advertising of mobile apps to more measurable world. This will eventually make the steps the user takes from the call-to-action to purchase smoother.
I believe Google’s model for Android will beat out its competition in the long run. Moves like this only go to reassure that.
Update: Here’s the WSJ story, http://ow.ly/3Qg5G
Update: The new market is here, market.android.com