And by the way, why do people keep saying "IOU" trading as if that's unusual? The fact is, ALL trading at exchanges is based on IOUs. If you trade BTC at an exchange, you're trading an IOU. If you trade ETH at an exchange, you're trading an IOU. When you finally trade LISK at an exchange, you'll be trading an IOU. You don't think coins are actually moving from wallet to wallet every time someone makes a trade on an exchange, do you?
Whatever you want to call it, "IOU" or otherwise, yobit trading is different from trading ETH right now at polo because LISK hasn't even launched yet.
In either case, one may not be trading the actual coins from wallet to wallet like you say, but in the case of ETH at least the exchange holds the real thing.
There should be some word making it clear that Yobit holds no real lisk. The word/acronym the community has chosen to use is "IOU".