Are the springs supposed to go upward?

[Joe Z]

Might sound stupid but every stock 3/4 ton 4x4 Chevy (including the half ton burb I have now) that me and my friends have had have front springs that arch upward with the rear arching downward yet the trucks sit level. Why is that? I have to ask because I've never see a stock one that didn't but again they're still sitting level. Are all the springs just shot or something? I personally don't care about it on the beater I have now but I'm curious. Thanks.