Very few platformers can pull off "hard" well because it can easily become re-playing the same 1/2 of a level for extended periods of time. This will result in

Very few platformers can pull off "hard" well because it can easily become re-playing the same 1/2 of a level for extended periods of time. This will result in users putting the game down, not telling their friends about it and game making less money. As for the open source examples my hunch is that they just wanted to make a mario clone and having play tested the game themselves throughout making the game didn't realize how hard the first levels were and never sat down and tried to built up any progression of difficulty that might match the players skills.