Good point.
There is a big difference between showing a little bit of upper cleavage, which is nice to look at, but not whoreish.
Showing it all is just unseemly.
This is all marketing tempest in a teapot.
The designer/maker found gold is just saying the dress is available. The fashion concious girls will go to the site and probably pick out some far more conservative dress. (then if dad is there, they will cover up a bit more) From one of the posts above the company does have more reasonable dresses which are not "club wear". They girls will be able to claim they bought the dress from the same company as the daring dress.
With that said its joke time (from readers digest pre-internet days)
Mom, Dad, and daughter are out shopping for a prom dress. After examining many dresses, the daughter wants to try on a strapless number. Mom does not agree, and so Mom and daughter are arguing back and forth while Dad waits in a nearby chair watching the debate.
Finnally Mom turns to Dad and says "say something!". Dad stands up, looks at the woman he married, looks at the little angel he raised and says "let her try it on, if it stays up, she is old enough."