I can see why you want to QT fish and corals but inverts? What are the chances of a invert introducing ich? If you have the QT running all the time then its not a big deal but who has that, not many.. The average person will pick up a few snail or shrimp and bring them home and acclimate and toss in the tank... In the perfect world everything should be acclimated, but in reality not many do. So I still stand by may answer that inverts do not need to be QTed.
I have never QTed anything and all is well, I may be dodging the bullet with this but I won't buy anything that does not look healthy.