Your question is one of the two reasons I love GNU/Linux so much, and will not go back to proprietary tools ever again :)
Even tough as a very average user myself I would never feel like compiling my own kernel, and would even less know how to do such a thing, I know it's a possibility and I know other users are doing it. And that is a possibility only because of the freedoms we the users are given by the GPL to do... what we want. To me, as an ex-lifelong Apple user (I started being their customer in the early 80s and only switched full time some 7 or 8 years ago to GNU/Linux) this is amazing and wonderful freedom.
Sorry if I have not replied precisely to your question but reading it I realized it was a great demonstration of what freedom is supposed to mean, and I felt like sharing it.