I always feel that the adage, as quoted, is missing a vital element which was inherent at the point at which it was coined - that element consisting of words along the lines of, "No matter how elevated their position in society may be".

I don't believe it was intended as a warning to the lowly to behave themselves, rather the opposite - a warning to the rich and powerful that even they are subject to the law, and not to fool themselves that they can do as they like by virtue of their wealth and power.

That's how my parents explained it to me, and how I've always understood it.