Paul Graham is wrong. There's a finite amount of wealth. His idea of "creating wealth" is simply expending energy in order to transform some thing into a more valuable configuration; both fixing a car and writing a computer program fall into the category of rearranging atoms into more valuable configuration. But energy itself is also a form of wealth, and there's only so much of it in the universe (and, more relevantly, on Earth) and only so much available to be used per unit of time.

In other words, you can bake another pie, but not without using some of the flour in your pantry and some gas to run the oven. Once the flour runs out, you're done baking pies.