Joe has it exactly. As I told Duncan in a separate note, I visit Norm Deno on from time to time at his home. All seed germination tests take place in ordinary garden soil. He surface sterilizes simply by a three application process of boiling water. This preserves the good bacteria below. The only fault in this logic is that if you transplant at the first set of true leaves anyway, there is no need for beneficial bacteria in the germination mix. I think the real benefit to Norm is that it saves money.