dual licensed software, including KDE and MySQL tends to be GPL + something else. Even among professional software developers, there is a lot of misunderstanding about the GPL and OSS. Most of that's down to genuine ignorance that there are issues to understand rather than anything intentional. It's not surprising therefore that there too misunderstandings here. On the whole, and unless we get down to the nitty-gritty, it's pretty straight foward.
In particular, GPL software appears in many many places, both comemrical and non-commerical, embedded in hardware and as standalone software. It has been said very recently that much of Linux's success was because the GPL "forced" companies, especially the big name ones, to contribute back their efforts. By contrast, the demise of the NetBSD project was because they _didn't_ use this style of license. The RO licenses is different again, and I can't be sure how it might play out, nor what might constitute "commerical", since there are a number of ways to play that game.