Regarding the Mother Theresa/Gates thing - it's an interesting question. I guess the difference is that Gates enriched himself in the process, whereas Mother Theresa didn't. He gave to others after his own wealth was assured, she spent a life picking people up out of the gutter.
That sounds more depricating of Gates than I intended. He is to be hugely commended for his generosity, and only he can know what it feels like to give so much away.