Why is the focus on money here? The impact of the technologies they create dwarfs any monetary contributions. What's the value of their technology on top of what the obvious sellable product is? That is, how much more valuable is their product to the user on top of what the obvious product would have been?
It affects some products more than others. Productivity tools have high leverage, as do protocols and standards, because they are means to ends. End-user products like food, music, sex (for fun, not reproduction), and housing tend to have little leverage because they are closer to the ends. That is, more of them increases wealth.
iPods are good because they let lots of people enjoy more music than before. However, it is probably on slightly better than the obvious product and in any case, the possible impact of a media player is limited.
UNIX (or HTTP or C) on the other hand is non-obvious and a fundamental tool impacting work higher up the value chain. These things have enormous impact on wealth because of the knock-on effects of the tools and they afford. Innovation and development is approximately exponential and, rarely mentioned, prone to get stuck in local maxima. Here be dragons. Would we have as powerful an Internet if it weren't for a few key UNIX design decisions? What would a Microsoft designed world-wide computer network look like?
Try this: how much time do you think people spend trying to align things in PowerPoint that could be made a snap with better tools (maybe 2007 fixes this)? Let's say 2 min per presentation. With an estimated (by Microsoft) 30 million presentations a day, of which say a tenth are newly created, that means 6 million minutes, or about 11.5 man years, are wasted. Every day. Because PowerPoint doesn't make alignment easy. Not to mention that it may limit people's ideas. What if other Microsoft products have shortcomings more severe than those in PowerPoint?
Microsoft products often strike me as worse than the obvious product, prospering because of lock-in/short-sightedness.
By giving his money away, I doubt Gates could ever make up for the value creation Microsoft has blocked. He would have to find something with enormous leverage that would otherwise not happen -- don't get your hopes up. Thus, though I hope he proves us wrong, Gates is down in my book as one of the bad guys. Things are looking better now, but we've lost years of exponential innovation. I bet Kurzweil is annoyed.