Here is my theory. I think in regards to keyboard I don't think people play differently from the default keyboard settings. That means the right hand controls Mario, and the left hand jumps. If you think about it, it is completely different with Arcade. Left hand controls Mario, and right hand jumps. To make an analogy, it is sort of like learning a song on a left handed guitar. On a left handed guitar right hand does the finger positioning, and the left hand strums. And yes at first a right handed guitar would be sort of hard to play than a left handed guitar,but eventually the right handed guitar is going to much easier to play the song with since most people are right handed.
