I'm pretty sure that's what they are relying on. I don't think anyone would spend $200+ knowing they are getting a non-gold modern replica. Especially when you can buy one for under $10.
I have no clue about the number of fake slabs and which there are more of. Not sure it's even possible to know. "Buy the coin, not the slab." - I hear and say this all the time. This will help avoiding mis-graded or misattributed coins, as well as some of the more obvious counterfeits that may be in a fake slab.
I believe that site's owner is operating out of China, where "anything goes" with regards to counterfeiting not only foreign coins and TPG slabs, but designer goods, DVDs, CDs, patented equipment and who knows what else.