I don't believe peak corn, someday we will raise a 15 billion crop, someday we will probably raise a 16 billion crop too.  I think you kind of missed his point there though, Steve.  Management and breeding have greatly minimized the impact from things that subtract yield (heat, corn borers, weed competition, disease) but base genetics have not really increased the maximum amount of #2 yellow corn which one plant is capable of producing in the absence of yield limiting factors.  Herman, with some help from Mother Nature in the form of a nice growing season, had figured out how to remove an awful lot of those limiting factors without the benefit of today's technology or a million dollar line of equipment.