Well I'm sure you already know this and that is why you had your program designed the way it was but the reasoning behind working those groups of muscles together is that they are primary and secondary muscles. For example when you do bench press you are working both your pecs and triceps. When you do lat pull downs you are working both your lats and your biceps, etc.
I used this same program with some variations for years. I am now doing DG training, which is great you might considering it.
Monday: chest, shoulders, triceps, back width, back thickness
Tuesday: Biceps, Forearms, quads, hamstrings, calves
You do not have to do DG training with these muscle groups I was just giving an example of another way to mix up your workout.....
Also you could do a total body workout one day, take a day off, then do another total body workout. This allows you to workout every muscle group 3 times a week.