Yes, the Ubuntu Software Center does have a section for paid apps. I do also believe that it should have a section on the main page for it too. The "paid apps" section is a great way for non linux developers to look at linux in a different way and see that there is a chance for them to make a profit. This will attract more developers (hello ADOBE!!!) to make applications for Ubuntu/Linux giving it more support. So some may think that the paid app is a bad thing for Ubuntu, but I believe that this will make it's market share grow.
Spot on Mason, free and open source is what a lot advocate, but I also have to agree with Bailey. Game and expensive app developers need a way to pay the bills while they are writing code.Should be interesting to see how well the Linux using community embraces the idea.
i do see both your points, but in the modding and gaming community when people put the man hours into a good game/mod then people play it a lot and the creator askes for donations to keep him "motivated", so i think the even open source still gets money even if the app is free.