The reason they have the 40 seat CRJ is cost. You see, Embraier makes a 40 seat version of their popular ERJ, and some airlines wanted a cheaper/smaller version. But, Bombardier decided to sell their CRJ with less seats, rather than build a whole new airframe. Apparently, it was cheaper for them to remove the seats and sell it as a 40 seater, rather than develop an entirely new airframe. When the airline purchases one, they have to sign an agreement not to put any more seats in them. I know this sounds strange, but that is why they have the 40 seat with the same airframe as the 50 seat version. I'ts cheaper for the airline, and for the manufacturer. Hope this helps..