I disagree. I have been working one major bodypart per week for years as a natural. I train three days on, one day off. I do 5 sets of ten for back, 5 sets of ten - for shoulders and traps, 7 sets of 10 - for quads + calves, and 8 sets of ten - for bi's, tris and forarms. I usually follow up every training session with 50 crunches, and some form of light oblique work. Due to an injury, I have been adding another set to my routine to make up for the missing abb work. I have always found that for me, variety is the key. I use core movements, but I make sure to switch up the supporting exercises every week. I rarely ever do the same exercise twice in a month - ( other than the core movements, bench, squat, pull up, deadlift).
Honestly, I dont try to overthink it. You could make an argument that you need to hit every bodypart twice per week, and I would counter that if you do it right the first time you will be sore until they day you hit it again.
I used to train heavy as hell and hit bodyparts multiple times per week. That style works, but it also led to a lot of injuries and nagging issues. With a very demanding job, I was not able to recoever, and I was always run down.