regarding Kahn Academy: I don't know. My 5 year old is competitive so the game mechanics work well. She's been using pbskids.org for years playing educational games, so it comes very naturally at this point. Also, she likes to learn :p Mostly I think it's her competitive nature.
Everyone/herself. Game mechanics: you earn points, you get badges... she wants to be able to say "look what I did." She likes "winning" and you can "win" in the sense of moving forward thru "levels," getting achievements, etc.
