The median is the 50th percentile including outliers, so the Bill Gates of the world to impact it. The mean normally removes outliers to get a better idea of the real average.
No, I think you may have this backwards. The median really is unaffected by adding a zero (or ten zeros) to Bill's income. All that matters is that if half the population makes less than Joe the plumber, and half more, then Joe is at the median. (There's a chance that if you shot Bill, then Joe's brother who earned 0.1c less would become the median, but this will be tiny, tiny effect.)
The mean would however be affected by such things.
