Something I should be worrying about?
I wouldn't say so no, supposedly most of the coins are in offline wallets and it would not be in Bittrex's interest to damage any coin as they would ruin their exchange.
As always though, we strongly recommend that you store all coins in a personal wallet unless you are intending to actually trade the coin. Leaving it on an exchange can seem logical but is does create the potential for attacks and if anything happens to an exchange, it is your coins that will be targeted.
and BTW, those two addresses are Bittrex's, not two whales' potential dumps. Those are like intermediate addresses where Bittrex keeps different users' coins together. But the fact that more than 60% of the coins are on exchange really really scares me...I hope everyone who has interest in Judgecoin in the long run could move their coins to an offline wallet, that's way more safer... I mean... think about vericoin on Mintpal.... and staking is always far less risky than trading :p