Then the total value of the currency should be equal to the total value of all the wealth in the world.

I'm not sure where Hal got this idea. The total value of the currency should be equal to the total value of transactions in a year divided by the velocity of money (average number of times the currency changes hands in a year), not "the total value of all the wealth in the world". Here's a simple example. Suppose there are two people in the world, Alice who grows apples and Bob who grows oranges. In one year Alice spends all the Bitcoins in the world to buy oranges from Bob and then Bob spends all those Bitcoins to buy apples from Alice. The velocity of money would be 2 and the value of all the Bitcoins would be equal to half of the value of products exchanged.