that will even out as soon as there are more big exchanges trading xel. For now only one big exchange trades elastic so no wonder big part of supply there. Go and count ethereum supply in every exchange it trades, you will also probably end up with high % of supply on exchanges. As more exchanges pick up elastic so does coin supply gets distributed around.
I hope so. With the ability to earn coins through forging in the wallet, to me, it doesn't make sense to store that much on the exchange unless you're actively selling.