Apart from the legalities, releasing the source also lets others build upon it. It's somewhat hard to produce quality tools when the information is so hoarded and likewise hypocritical to hoard information when most of the inital information came from a GPL'd program.
In the end it really depends on the users. Most come from a windows background and have little clue as to what opensource means or how GPL'd code works and therefore don't push the issue with the developers. GPL is basically saying "I'm giving you this information on the promise you won't try to monopolize it", that is that you can do whatever you want with the information so long as you share the information, free of charge.
But what if you have no desire to program?
The way open source works and the reason it's so popular is that programs released as part of it evolve quickly. Instead of just one programmer working on the task you have dozens from all over the internet studing the code, fixing and improving it. Even if you don't code yourself, by pushing for open source you're helping push for a higher quality program -- something to think about the next time the program doesn't perform.