An interesting question. Begging the next, why even use a straight blade in the field when the average trooper is overequipped with other tools?
Unless your MOS requires serious bushcraft, a large field knife is redundant, as pointed out earlier. Most troops don't use theirs - ref: the Civil War comment on large bowies. Historians and accurate reenactors know that fad died once you hit the long march. Clasp knives and short 4" utility knives were much more predominant, and the today's soldier is no different.
Another point is that once the large knife was no longer a self defense tool, the experts at bushcraft shrank it down to a reasonable size and debated the use of the axe. leaving us the Nesmuk and others as an example of useful knives for the field.
I like and own a Randall and other camp knives, but they stayed home when I went to the field, especially when I had gained some experience, and that's what I saw others do, too.
I would like to hear from troops in Afghanistan what tasks they use their large knives for on a daily basis, coated blade or not.