As for Lua I think it is rather chicken:egg. Lua is popular because it is used by mod APIs, or is Lua use by mod APIs because it is popular?
My own experience is the former. I think it is a horrible language (in that I argue many others are better) and especially difficult for new-to-programming gamers with great ideas to pick up. Haskell or Erlang (or Java or C#) with type-safe APIs would be much more educational for them, and provide better support IMO.