We don't (and don't need to) maintain packaging for every OS distribution out there, but we do need to make every effort to make our software easily packagable for any modern OS. We can do this simply by following best practices such as careful dependency management, meticulous license compliance, automated build infrastructure, standard version numbering, etc.
If this is done well, it is then trivial for package maintainers for various OS distributions to create nice, maintainable packages for any GNU/Linux (Debian, Ubuntu, Fedora, Gentoo, etc), BSD (FreeBSD, NetBSD, OpenBSD, etc), Mac OSX (native, fink, etc), Windows (nullsoft, wpkg, etc), and any other OS that comes along.
We don't need to be perfect (people will submit patches) but we need to make a serious initial effort.
Anonymous
I think it makes sense to have packages/installers for the following operating systems in order of descending importance: Windows7, Debian (Ubuntu), RedHat (Fedora), MacOS. Win7 and Debian are probably necessary.