I'm not sure, but as you can't withdraw STEEM from Binance, there is no possibility of arbitrage between Binance and the other platforms, which allows this kind of differences.
Once they enable withdrawals again, it will allow people to buy on Binance and sell on other exchanges, bringing the difference to zero.

It's not really that they're manipulating the price, it's just that nobody wants to buy STEEM they can not withdraw or power-up or do anything with in fact. So bear in mind that once Binance allows withdrawals again, price will go up on Binance (as people will buy for arbitrage) and go down on other exchanges (as people will sell what they bought on Binance a few minutes earlier). I don't really think they're manipulating the price, but I'm sure they will be the ones making the most of the arbitrage opportunity as they will be the ones to know exactly when the withdrawals are possible again.