Why do games for Facebook have to be about 622 pixels high?

Question

I am wondering, why do games for Facebook have to be about 622 pixels high?

Answer 1

Think about the general user base. A lot of players will own laptops that are about 768px high (most common around the 15.6" range of screens) so making it about 622px means that game will fit on the screen.

There are some games that have a fluid canvas which resizes the game area to fit the browser window which is quite nice.