What's the difference between "uname -r" and "uname -v"?

This is absolutely normal and expected. kernel-release will always show the actual version number of the used kernel. kernel-version however will print a more specific string with the actual release date. Its format depends on which Linux or Unix distribution it's run on.

You can find an extensive list of examples on Wikipedia. For example, in OS X, the kernel-version will be not only the release number, but also the release date:

Darwin Kernel Version 10.8.0: Tue Jun  7 16:32:41 PDT 2011; root:xnu-1504.15.3~1/RELEASE_X86_64

While the kernel-release is simply the release number:

10.8.0

You can even check /proc/sys/kernel/ for the things uname(2) will look up when it's called by uname(1). This would be:

• /proc/sys/kernel/version
• /proc/sys/kernel/osrelease

Don't think too strictly of "version" as just a version number.