I really hate the "over-qualified" response. It's completely idiotic.

Do you want the best you can afford or do you want something less good?

I choose the best, but that's just my view.

Retention may be a valid point, but I had this response once for a high salary position and it just doesn't make sense, retention is only a problem if you're paying too little as this is the number one factor for changing jobs among ambitious IT pros. Hence why when you get in to higher salaries you move around less.