I actually work in a CD store (new and used) and we have a handful of regulars who come in and want to inspect certain CD's to see where they were made.
They're usually looking for German pressings of certain CD's, or Japanese issues, or whatever. I don't really know what but it's annoying all the same because they're never what they're looking for
Obviously, most Cd's only have one version, but like you said something like Pink Floyd DSOTM has been issued many times and each time "remastered" etc etc.
The newest one is an SACD hybrid. So if you have an SACD player you'd probably want that right? Sounds fine to me.
But the newest version doesn't always mean best especially with all this "loudness war" stuff going around.
I have an example I just came upon the other day that actually has me concerned.
The Doors-Very Best Of 2CD on RHINO.
I have 2 versions of this. One is from 2000 and looks like this
The other is 2007 and looks like this
The second one was remixed by the band (obviously minus Jim Morrison) though it doesn't really say that on the packaging or even in the credits and they sound completely different, and odd I'd say. Comparing songs back to back the difference is major. Some are in completely different octaves! The newer one actually sounds less defined and overly reverberated, while the other sounds too up front and clean!
So there you go, in cases where there more than one option for a particular recording there can be a huge difference and it's possible that without hearing both you wouldn't ever realize!