The fact that one exchange holds close to 1 million or 1/21 of all BTC is scary in itself.
But hey, don't let people tell you that Bitcoin is centralized.
Bitcoin should stick to its promise - decentralization. P2P + Ripple for fiat onramp/offramp is the only solid solution. This will remove speculators from the picture as they won't be able to conduct High-Frequency Trading and will keep large investors off the market, too, as it won't be so easy for them to acquire large amounts of bitcoins.