Paul Eggert wrote:

However -- in case this comes up -- as far as I know we have never relied on their case-sensitivity, and there are no plans to do so.

...which is a good thing, given that in the Olson code they're file names, and in OS X, which uses the Olson code, the files are probably going to be stored on a case-insensitive HFS+ file system. (Not that any good reason to rely on the case-sensitivity comes to mind in any case.)