We always had only numbers in high school. (I miss the S, I, & U system of elementary school. Hehehe) At college, you couldn't get an A+, but it started with A, then went down with the minus/no sign/plus system. I didn't mind it because I always got pretty solid A's.
I think most of the high schools people came from at my college had this same system, because no one ever really mentioned it as a problem or advantage. It just was the way it was.