Version Cue's purpose has nothing to do with "versioning between different releases of Adobe apps". That's what PDFs are for (compatibility for printing). Adobe doesn't factor in native files being transfered...if it happens, they expect everyone to have the same version of the app needed anyways (the latest version, that is). That's why they give the shops the ability to participate in a program that provides the latest and greatest Adobe apps for a set fee yearly.
VersionCue's purpose is to help designers who have multiple "versions" of the same project (a document, an image, a business card, etc.) easily manage things, as well as associated files for that project. It is a FILE MANAGER, specifically where "version" = "revision" of a singular file/project.
For example, you create a flyer for a client in InDesign. During the design process you'll wind up with multiple copies of this file that you name differently for organizational purposes (flyer_roughtdraft.ind; flyer_a.ind; flyer_b.ind; flyer_c.ind; flyer_1strev.ind; flyer_2ndrev.ind; flyer_rejected.ind; etc.) and possibly have scattered through a series of folders you create on your HD. That process (creating the directory structure) takes time to do, not to mention is a big pain in the arse when it comes time to find things later on (note: VersionCue was initially released with CS, back when Spotlight wasn't even a dream).
VersionCue lets you save the file as just "flyer" and track any changes and variances over the life of the project. If you're in a team environment it can also aid in tracking changes and revisions made by each team member. Anyone who has done design work will see the advantages of it immediately and also realize that it is
very useful for a singular person..
I remember sitting at a design symposium Apple put on in Nov of 2003 in Cincinnati—during Adobe's presentation of the features of the soon-to-be-released CS apps—and thinking this (VersionCue) was going to make my life so much easier as the Adobe rep talked about it. Probably would have, only I never got around to completely switching over (old habits are hard to break). I use it maybe 20% of the time, usually on large projects only.
What I wrote is a very basic and quick description...you should either try it out yourself or read Adobe's literature on it for a more concise understanding. I've only used the version included with CS, but from the looks of things the newer CS2 version is much nicer.
More information:
Adobe white-paper on Version Cue CS2 (pdf)
Online Tour of VersionCue