Us dollars, Euros, etc. aren't something of value in return? They are. All that trading for USD is the real economy. It doesn't need to be trades for drugs, porn, or socks to be real economic activity.
No, it's not the same. If you have to exchange money every time you want to buy some real goods you can just as well get rid of Bitcoins completely and stay with USD and gold - it's less hassle and less risk. "Economy" based solely on generating numbers and selling them for USD is not sustainable in the long run.