I guess I would be interested in an independent source of that information. I'm not totally dismissing AG as a credible source of information for products they carry, but I don't know who writes the ad copy.
I can say in my internet search for natural sea sponges a while back, I found no information to confirm that statement. Several sources citing the superiority of the praising the qualities of the Mediterranean sponges, but it seems that the rest were lumped into a common group. <insert dunno smilie here> I'm no expert, just relying on the information I have available.