The specific reason for Linux, though, is that I think most of the interest in Linux lies in what you can do with it, rather than the latest filesystems or other kernel hackery. That is, most people are interested in running applications on top of Linux rather than in running Linux qua Linux. So most of the Linux juice will be in the "Applications" track (desktop GUIs, SAMBA, etc.), and that's where I'll throw any system administration stuff as well.
Am I high? Is there really an audience of many thousands of people who will come to OSCON to hear a day or two of kernel hackery talks?