I just bought "Defence Grid" for $2 on steam. It's not much money, but I wouldn't have paid any more, and wouldn't have even bothered to pirate it. I probably won't even play, but my brother uses my steam account and he might check it out.
My point is that $2 is a good impulse-buy price. I won't even bother to check a demo or reviews at that price. So that's $2 more than they would have gotten.
I'd be interested in seeing their total profit binned by price.