It's actually the definition of applying a texture to a leather that makes it "corrected grain". A corrected grain leather simply means that it has an artificial grain applied. Often this is done to hide the blemishes in leather that does not meet the cosmetic standards for use as full-grain leather. It does not necessarily mean that worse leather is used. I also understand that corrected-grain offers better water resistance.
The Duke and Gridiron are not calf-skin like many other Allen Edmonds shoes, but are made of steer hide such as used in footballs. I'm not sure how this affects water resistance, but the leather is notably thicker. Also, I'll note that my own Duke loafers have developed a cordovan-like roll to them, rather than calf-like creases.
Finally, in terms of the quality of the leather, it's worth noting the following page from Horween which says the steer hides they purchase are "generally considered to be the best available hide": http://horween.com/101/by-request-whats-the-difference/