Tim,
I think you are right. I hunted in central Mississippi for many years. Huge deer and lots of them. But, unlike the Northeast, people in Mississippi don't think "hunt deep woods." Soybean is the no. 1 crop in that state, and it is not unusual to see 200 to 400 acres fields of it, surrounded by very wet densely wooded swamp land. People hunt "the edge" by setting up a stand about 10 feet back into the swamp woods, and watching the field, plus the tree line that they are in. Shots are long, and the 7 Mag and .270 Winchester rule the roost. The .300 Winchester Mag is very common as well.
So, I am not surprised that the .35 Whelen was a big seller for the primitive season. People are after the range, not the knock down power.
I am also not surprised that there wasn't enough demand in Mississippi to justify a special run of .35 Remington Handies. The .35 Remington is not held in high regard in that area, and the phrase "lever-action" means a .30-30, which I believe is issued to every boy in the state at age 14 :-) It is kinda regarded as a boy's rifle!
Best,
Mannyrock