I see no reason why they need to moderate their gallery since it doesn´t claim to showcase professional work only. It is just a user gallery.
Something I really like seeing, is how much enjoyment people get when using Marvelous Designer. When they post their images to the gallery ( even if they aren´t very good) , it´s something they had fun doing, and worked hard at.
It doesn´t matter that the image next to theirs was done by a master artist or not.
I think some people are lacking that feeling. They complain about things they can´t do, instead of marveling at the things they can.