The problem with using all of the corn as a feedstuff is that we have way, way, way, too much corn.
We produce too much food, including meats, and exports are absolutely critical for agriculture.
For example, did you know that the pork industry was only 90 days from total and complete collapse last spring (2010)? The pending collapse was due, in large part, to the mountains of surplus corn, more than could possibly be used as feedstuffs.
We would have lost well over 90% of our pork supply had that happened. The producers hung on by the skin of their teeth.
NVDave says "China et al are buying HUGE stocks of our crops and taking away all prior assumptions of year-to-year surpluses (called carry-out in farmer lingo)."
That makes absolute sense when I look at food prices & our family food budget.