I never noticed that!!! However I am not surprised. Both spellings are actually correct. LOL! I'm a bit of a history idiot so I will try my best to explain. Bare with me as it is very interesting:
This goes back to the Crusades. In Europe soldiers discovered a game played by the Arabs and Turks which was called "Little Wars". In Italian it was called "Garosello", and in Spanish "Carosella". So there you will notice the ONE "R" in the name. That was basically where you see Men on horseback with a lance and they spear a ring which was hung on a tree with a colored cloth on it. You think of this game being played when watching a jousting tournament. So the Crusade soldiers took different variations of this game back to their own home lands. In France (The Little Mermaid and King Triton being French) the variation of that game became known as "CARROUSEL".
So to assist in the training of this game, and to make sure the horses didnt tire, they created carved wooden horses and chariots, and suspended them from a pole. The rider would attempt to catch the rings while another person pushed the rider and carved horse. This is where the beginnings of the carousel originated.