The sum total of the bitcoin economy is all that is for sale, including USD. From the point of view of an owner of bitcoins, they are all just products being offered for sale.
At present the bitcoin economy is heavily weighted towards sale of paper with presidents on. It makes no difference; the economy is flowing, and as long as that sustains, bitcoin will survive.
I don't think that's a terribly useful measure of the size of the economy. In any case, the problem isn't just that most of the Bitcoin "economy" involves buying bits of paper with presidents on, it's that people are getting Bitcoins by selling bits of paper with presidents on in the hope of buying more bits of paper with presidents on with them shortly after, and that's just not sustainable.