I agree, there are lots of history where people who left their coins in exchange lost everything. GOX and Cryptsy are the bigger one, and there are some small exchanges too like sharex that just close and run with their client's Coin not saying the one posting this message have First hand experience of losing coins to an exchange/trading platform that shutdown.
Yeah true, I remember before I never thought that cryptsy will be shutdown, I was shocked actually, but I learned and that is, it doesn't mean the exchange is company it will long last,..no its not like that just like what happen in bitfinex its a company and many people invested to that exchange but it shutdown too.
But it were running without license, and the most of the people didnt know it, i just trust poloniex, and sometimes i let my all funds there, but as are always less then 0,10btc im not taking a huge risk. All should know that the most exchanges hasnt license to run, soo the result will be a hacker attack or closing doors.
I even dont even know such thing that most exchangers doesnt have a license to run. I trust also poloniex too but same as your i really dont put up too much money on there or any exchanger like c-cex etc. . I lost also money on bitfinex too for about 0.5 which still a waste of money but i accept already because any investment would have the risk not only to the coin but also to the site that you have invested your money on.