That's ridiculous. You don't need to write to them all. Debian-based would be a good start and would embrace the largest proportion of Linux users.
I agree. Many Linux distros are based on Debian (including Ubuntu and Linux Mint), so if you write Rootsmagic into a .deb installer for Debian it will work on most linux distributions. The other distributions like Fedora use .rpm installers, but they aren't used as much as the Debian family. However there is an even simpler method used by Firefox and Minecraft for other distributions.
What you do with firefox and Minecraft in some distributions is to download the app compressed into a tar file with all dependencies it needs. So get it working, compress it into a .tar file, and let people download it. It's that simple. You wouldn't even need a .deb or .rpm installer.