To most of the people on this forum, whilst maybe relatively new to corns, yet not necessarily new to keeping herps... that probably makes a lot of sense Rich.
It certainly does to me.
But, aimed toward the uneducated, I tend to agree that it gives the impression that the animal as "something special" over another given animal (of the same species). You walk into one pet store that's got a striped-anerythristic labelled up as "corn snake", and another one down the road who's got a fairly identical snake labelled up as "designer corn snake" at twice the price...
Ok, so yeah, it is a marketing ploy. Just like "designer" clothing. but like Missmonkey said... all those idiots who are just bothered about a brand name, or things being "designer" are the type of people who'll fall for it, make the pet store an extra few $$. The pet store knows anybody who falls for the "designer" trick can be told, and talked into buying, anything.
Those are the kinds of people who buy iguanas because they "look cool" then leave 'em living their life out in a 20g tank, and wonder why it dies after a couple of years of being fed on crickets and monkey chow.
From a reputable breeder, "designer" can imply, as you said, that it has been selectively bred over several generations to achieve a desired appearance. Unfortunately, if a pet store thinks they can use a word like that somewhere, they'll do it, and abuse it.
As well as above, it devalues the "designer" label previously applied by you as a breeder Rich.
Just look at Leopard Geckos... very few serious breeders have them labelled up as "designers". They list the exact morph(s). Only people I've seen mark them up as "designers" any more is the tables at shows where the leos are simply being sold for somebody else and they know absolutely nothing about 'em, having 50 hatchlings together in a 10g with a sand substrate, and no dry or moist hide - ok, not essential for a 2 day show, but still stresses 'em out. I saw a LOT of half-tails and nipped toes in those kinds of tanks at Daytona over the weekend.
I just think to those who've seen it applied to animals before, as well as just personal opinion of the word, it really has the opposite of the intended effect and degrades an animal if not used very carefully (and by the right people).