Richard Branson once pledged $3 billion of the profit from his airlines over ten years towards efforts to combat climate change. If his airlines didn't make that much profit, he said he would take it from other parts of his business empire. When someone checked up 8 years in, he'd managed to give $200-300k over those 8 years, and the forecast for the next 2 years was not looking good.
Two things to take away from this - 1) that Steve Jobs' 10s of millions is not bad compared to his peers, and 2) that so far Bill Gates has said he will give $500M for this particular cause, but what really matters if you're going to compare this with Steve Jobs' donations is what he actually gives out in the end. (not that I think Gates has as bad a record as Branson).