I personally believe drop eye is genetic, and yes, asian aro get it quite common.
I believe that ALL arowanas in a tank get DE at some point. And when people say thei "entire life", how long is their entire life? Fishes are like us, they get old, and their muscles, in this case the muscles holding their eyes straight, are gonna get loose.
I don't think somebody is gonna post a 35 yo Arowana to prove me wrong...