well, I think that could be a philosophical discussion but, on my experience working on the private sector, marketing does a lot more than just selling stuff: marketing defines the products and services to be sold based on feedback taken from market needs.
in our case, I think it should be a marketing function to define which features must be available on the next version of our product and to manage a good communication strategy with the possible buyers of our services. I think is a bad idea letting developers do this because developers most of the time are going to take decisions based on technical issues and not on market needs.
that's why I think we need a strong marketing team with people knowing their business; obviously I'm not one of them and this is only my opinion.