"I don't know, sells milk, well I may just have a use for that domain in promoting my product."
So what? I can drive around my neighborhood and somebody might have beat me to the last breakfast sandwich at the Starbucks and they might take one bite and throw it away. The world doesn't work by the fact that you or anyone might have a use for something better than someone else. You pay the money, you buy something, you decide what you want to do with it.
I think what you don't understand is that there is a business model built around buying and selling domains. And there is nothing wrong with doing this even though it upsets many people who just think "it's not fair!".
With your hypothetical company that wants that domain what happens if what you are doing with it (for your "little" store) doesn't match up to some big dairy when they think they should have it. Are you going to just give it to them or would you try to make money? More importantly you seem to assume that "milk.com" would be available right when you want it. The truth is the owner could have sold it years ago to someone for $5,000 that is using it for something and then you wouldn't get it anyway.
I'd like to say that I agree that he, for lack of a better way to put it, is being "a dick". But the truth is that's actually good if you want to buy it because it will scare many people away who could buy the domain in the past who believe his (what I feel is) false bravado.