Thingiverse does allow posters to control the licensing rights to their designs, which is a nice feature. However, I think that it is a very disruptive model.

I understand the concept of open collaboration. You can enjoy the free designs posted by everyone else, if you allow others to enjoy yours. As long as everyone continues to cooperate, the model will continue. However, I do feel that there is tremendous potential profit within the site, since it is so established already.

However, it is also important to remember that the site is run by Makerbot. So the current model makes perfect sense for their business model. Since potential customers looking to buy 3d printers are going to need files to print. And the popularity of the site has to drive customers to them.