I don't think there is a difference. I know in the U.K. they refer to acne, pimples, and zits as "spots". It is their slang for it, maybe you've heard people from there referring to their pimples as spots.
I'm from the UK and yeah, over here we call them spots. People do seem to think spots and acne are two different things though. For example; ''No, he had acne! Not just the ocassional spot like i have''. To me its exactly the same, a spot is acne.
It doesn't help when commercials on UK TV say; ''Now try Freederm. For freedom from spots and acne''.