There are two types of currencies in the world: time and money, and most of us trade one for the other in various forms (pay for convenience, or spend time working for a paycheck).
For the richest man in the world, he has all the money he'll ever need, but just like the rest of us, he only has limited amount of time left on this planet. Yet he is fully devoted on spending that form of currency, which is infinitely more valuable to him than even others, on the causes he believes in.
That alone convinces me on his sincerity and his true desire in making a difference.