I remember seeing once a documentary about why some buildings are representetives for their cities. They gave as an example the Eiffel Tower, which you can basicly represent it out of 3 lines, it's just an A shapped tower. They exemplified other monuments as being easily represented within 3 lines. Point was, becuase they could be represented within 3 lines, than they would be easily remembered by people, and actually attract people through their simplicity.
While watching MLP, I started thinking about this. You can't draw them within 3 lines. No, but between them, there are only 3 elements which sets them appart from one another. Their color, their mane shape and their eyes. I dont count the cutie mark as being something repesentetive since it's rather small. So I believe that's one of the reasons why these characters are so appealing, because they are easily recognized and what we perceive in them is easily digested by our brain. Furthermore, some people claim "omg, MLP sux, the main characters have only 2 dimensions", but I believe that it's all for the best actually. You have 6 characters which are easily defined visually, whom also have very simple and extreme character types => even easier to be defined !
Also, the facial expressions are so awesome, they really managed to represent emotions succesfully. Personally, from a graphic point of view, MLP is amazing !
