Developers are usually interested in solving interesting problems instead of boring everyday stuff. Of course they don't want to be bothered every day by students with installation problems who haven't read the README file. But, hey, I'm a developer, too, and I won't contact support without in advance having tried hard to solve the problem.
I think nobody claimed that. (Someone put it in those words a while ago: nobody ever got to see my C64 BASIC exercises. Today's schoolboys' playpen PHP accidents are sold as open-source e-commerce solutions.)
If the bug doesn't get fixed, nobody deems it important. For OSS you could at least try to resolve the situation if you disagree with the maintainer's view.
That doesn't necessarily depend on the kind of software they sell, it more depends on the size of the company. A small company that is happy to have found a big one buying their stuff will be more cooperative than a big one having sold to a smaller customer, and knowing that the customer has no choice. Especially when there's an ocean between the latter two.
Stefan