Something else: The other day someone mentioned about the DRK allocation to various wallets and that Cryptsy has something like 400-500k DRK (?)... so, in this scenario, an exchange of that size can create 400 master nodes as a way to gain "interest" on their money despite the hot-wallet risk. Even if they only used 50% of their DRKs, it could be 200 nodes - which would be a sizeable part of the network under control of only 1 party. That would require quite a lot of laundering depth to avoid the chance of hitting a cryptsy node every single time.
Good point. I wonder if holders would then want to run multiple nodes themselves, withdrawing from Cryptsy. I know I would but I am a bad trader.
Furthermore, if it was discovered that an exchange was keeping a large majority of funds hot, do you think users would keep their money there? People are excessively stupid so it is likely.