I too have not been able to determine a significant difference between the two, but I don't deal with ladders everyday in my work (altho I have at least 8 around from 4' to 28' extension). Kinda seems like Chevy vs Ford provided you stay within the same material and weight rating, but I'd bet some have certain trays or pockets that painters or other pro's prefer.
One of my favorite ladders for in-shop projects is a dual-sided 4'. We used one of these once when building a wireline truck to repeatedly access the rear. Nice, heavy duty, not too big, and you could walk up either side. Very practical in certain applications like this. Takes up more room when stored folded though as it doesn't fold down as small. I actually ordered this from HD online many years ago (best price at the time) and they shipped it UPS in a big cardboard box.