The price of a GH/s depends on both the current and future values of the difficulty. The price has been rising at cex.io because future difficulty is now expected to be less than previously expected. This has caused the price to rise even though the current difficulty is still rising.
Despite that, the price at cex.io is still too high. It is unlikely that anyone holding shares at the current price will make a profit.
The price depends on what people are willing to pay for it. It's those who check the difficulty that affect the market the most. Otherwise, it's not necessarily the difficulty that changes the price.
That being said, it is true that anyone that holds the hashes for a long amount of time are most likely the ones who will end up getting burned, no questions asked. It's the traders that will actually make money.
It's like the stock market, but in an opposite trend. The stock market normally rises over a long period of time (unless they are 100% useless it get thrown under the bus of crappy management) and can be sold for more than they worth, while possibly paying dividends to the holders. Bitcoin is the opposite. Price decreases because of the difficulty increase and thus prices will decrease, etc.
So Bitcoin cloud mining is the opposite of the stock market. And it's opposite from the overall economy most anyways...
