All aro's seem to have the ability to GET drop eye, I've seen it on all types, golds, reds, blacks etc... however it does appear to be more common in silvers, as the vast majority seem to be affected by it.
It can't be from looking down for food, there are many people who have other types of arowana that have silvers as well, and it isn't like they treat them differently. Or perhaps it IS from looking down for food, but the silvers are affected by that much severely and develop this condition.
It all leads back to being something inherently to do with the make up of the silver arowana in general. We all take pride in our fish, and we wouldn't treat a silver any worse than a red or black per say. Or I would hope not. We do not opt for cheaper diets for the fish, nor do they really eat anything that different. So we can narrow down the field to saying there are perhaps many contributing factors, but at the end of the day it boils down to simply being that the silver aro for whatever reason does not handle these issues as well as his colored cousins and forms this condition much more readily and consistently.