I think that everyone who develop and share its software do this to achieve profits in long term. For one person satisfaction can be a profit. Somebody else wants to earn some money. In the case of Windows Phone developer can earn money by selling its application or publish ads. Both ways are extremely simple to implement. The only one problem is to find great number of people who will use our application.
After looking at the analysis of application on Windows Phone Marketplace, we can discover that list of people who have succeed is very short. Moreover, we cannot find statements about their success very often.
For this reason I would like to encourage you to spend some time and watch interview with Brandon Furtwangler. He is one of the people who achieved success on the Windows Phone Marketplace. Together with family he has set up Four Bros Studio LLC. This studio developed Taptitude game – one of the most downloaded game on Windows Phone. Above you can find mentioned interview.