Isn't this what happens when something is available to be bought and sold? We all have a natural desire to buy low and sell high. I wouldn't call it market manipulation unless it's a whole bunch of people with extremely deep pockets (like banks, for example) getting together and dumping the coin all at once to make the price go down.

But buying and selling to turn a profit is what everything is being used for nowadays. Bitcoin is not practical enough to be used as a currency (yet) so in the meantime takes the shape of an investment vehicle. It's listed as a commodity because it is being treated that way by investors. Finite supply, fixed price, etc.