Tim:
In the last few days, I had read a page discussing a more universal single /etc/release file, that would use the one filename for all distros, and have parameters inside it that were specific to the particular release.
T.C. Hollingsworth:
That would be /etc/os-release: http://www.freedesktop.org/software/systemd/man/os-release.html
Yes, that was it. Sounds just like what they original poster wants, but probably hasn't been implemented enough for them to use.
But, to my mind, if I was having to support numerous OSs, rather than trying to poll package managers databases, and make guesses about which distro it was (and release version, etc), it'd be far easier to find out what release file they each use, and search for them (in the absence of a universal release file). It'd only be one file per release, and surely each release file would be unique enough to identify it clearly.