Ryan, technically you're correct but not really. Since ALL models will print slightly different even though they are the same (in the Pro series aside from the 17"), you would still want to make a profile for each.
Realistically, all 4 sizes should be the same in print quality since it's the same exact head and ink set, but since it's not guaranteed to print the same on every model even though they are built the same, the custom profile is best to make it match closer to each other but they should come out fairly close.