Marketing is not a simple job. I don't really know how to do it well (in this company, that's a problem for other people). It deals with things that are hard to quantify, but that doesn't make it any easier or more important.
You seem to miss the fact that this is an opinion of sales and marketing, not just sales. If you think there's no difference, you're unqualified to have an opinion. (Marketing is about setting up an environment where it's easier to sell, sales is about actually selling the stuff.)
Your attitude is that the developers should dictate how sales and marketing should work, and sales and marketing should spin what the developers like. This is very much like having sales and marketing set development deadlines and vague and partly contradictory specs, and expecting development to come up with a product that conforms to the specs on the given schedule. If you (correctly) think that's a recipe for failure and other bad things, why would you expect sales and marketing to work well when given orders from developers?
Basically, if you can't trust the opinions of your marketing guys, fire them and hire different ones. They're the experts here.