If I'm not mistaken, I believe this body parts combination began back in the late 70s early 80s, as one of the most popular bodybuilders back then Mr Frank Zane (Mr Olympia) used to combine them that way. The idea was to take injury prevention into consideration here, since the shoulder joints would have warmed up well after doing the chest, and the triceps/elbow joints would have also warmed up after doing some shoulder movements.
Now everyone has their particular reason for performing their split (if there was going to be a split) in a certain manner. There's not much that is an absolute correct or an absolute wrong way in the sport of bodybuilding. The ultimate program for each and every bodybuilder out there is exactly the same (even though it's not the "same") and that in a word is called: change. A change from what you're currently doing that is. As someone once said, the best program for you is the program you're not doing.
Bodybuilders are humans too, and humans as a rule do not like change, especially when something has worked for them for a time. Sometimes it takes a nudge from a friend to say hey, have you tried this or that, and before you know it, you're on a roll and a whole new program... with new added muscles to show for your (changed) effort.
A split, even one that you don't think much of, can work wonders for someone out there. So my advice is to always keep your options open and never be so rigid in either your thinking/belief or in your training regimen. A tree that bends with the wind will always outstand a solid and stiff tree that is a disaster waiting to crash down when enough wind (gale force) hits town.
Flexibility in both mind and body would always win the day over rigidity.
As the late Bruce Lee puts it: "be like water my friend", after having demonstrated how water can take the shape of everything it is put into.
Fadi.