I first soloed in a PA12... They are the super cruiser.. The PA-18 is the super cub. If you have ever flown a plane that is exact scale then you would not be asking this question. An exact scale replica flys like crap. Every designer has to trade a few scale lines in order to produce an aircraft that is airworthy.

Also there are many modifications to the full scale aircraft. Clipped wings, longer wings, slotted leading edges etc. There are many options that the designer has to play with and still keep the scale lines.