High 4?

Why do cartoon characters only have 4 fingers on each hand?  I noticed this a while back while watching Family Guy and figured it was just the way the illustrators draw them.  Then I noticed a lot of other cartoons that do the same thing.  Why?  To use less ink?  It's easier to draw 4 as opposed to 5?  It's Cartoon Law? This, folks, is what keeps my up at night.