Addons are loaded alphabetically on NTFS filesystems, which, as the filesystem used by Windows, covers the vast majority of users.
I don't know what the Mac filesystem does, or Linux filesystems...
I use a Mac (and a Windows machine btw).
Basically the alphabetical part stands on Mac as well. Since you can't play WoW natively on Linux, you'd be stuck with Wine or a VM with Mac OS X/Windows, you'd end up with the default situation.