It seems to be only BTC and ETH at the moment... Hopefully they'll expand to other ALT's again soon.
They will, that's what made them big. I think it's more about checking if everything works fine and no additional backdoors are installed.
Better to be safe than sorry
I do appreciate the fact that they want to beef up their security. Eventough for a service like this, not many people risk losing their coins (except the exchange themselfs), it's still a good idear to have sufficient security.