Question on cmis:objectid

G'day TC,

Quick question (though I suspect the answer may not be ;)…

Why are cmis:objectid's version specific?  By that I mean, why do they refer precisely to a specific version of a versionable document, rather than a document in its entirety?

The background for my question is that this trips up most of the client implementers I work with (3 in the last month alone!) and when asked to provide an explanation of why this is better than alternatives (e.g. having cmis:objectid's refer to the object in its totality, with versions of that object accessible via some complimentary mechanism) I'm at a loss.

Thanks in advance,
Peter