There is a very interesting thread going over at ADI Forums about yeast making that has drifted into some interesting territory about sour mash and lactobacillus. I especially recommend the posts by Denver Distiller. The stuff in my posts you've seen before.
Denver Distiller, for example, explained sour mash as a cheap and readily available source of acid to condition the mash pH and also a cheap source of nearly perfect food for the desired yeast strain. Likewise although there are no active lactobacillus in the backset, there is lactic acid.
The other interesting idea being advanced is that the early association of geographically-specific yeast strains with the corn-based whiskey that came to be called bourbon gave Kentucky-based distillers an advantage over distillers who subsequently tried to make bourbon in other places.