As a designer/programmer, I completely agree.
As a programmer, the idea of saving multiple copies of a file with different versions numbers just sounds awful.
But when designing in photoshop, theres rarely a need for a full version control system since I usually only have 5-6 PSDs of each iteration per design (or logos/sites/etc) and at that scale its easily manageable.
If version control was built into photoshop, it would be nice but the important thing is its not a need I have and I wouldn't necessarily seek this type of product out.
I feel like the word "version" means completely separate things to a programmer talking about (d)vcs and to a designer talking about mockups. To a programmer, version control is more likely to mean revisions of the same file as it evolves and is changed. To a designer, a version is a distinct mockup that represents a new look.
(Sure, a programmer may rewrite something, and a designer will tweak something. But, even then. Different words are used to describe what took place.)