There are more than 2 500 000 XST on sale on Polo and another 400 000 XST on sale on Trex. This is almost 12% of the total XST. Why people keep so many coins on Polo and Trex? They can be hacked anytime as it was the case of Mtgox, Bitfinex, Cryptsy. Would it be better to keep coins securely in wallet and receive 20% annual ROI?