Well, he's in a higher bracket so he's paying "less" to reduce his taxes...
Aren't you also limited to deducting 50% of your income? If Bill 'went to the limit' and no further that would mean that he must have made $58B in the last 6 years (based on having donated $29B)....unless of course he gave most of that after August of last year....still an impressive amount of money to make in a 6 year period...and yet his net worth hovers at $50B....
Yes, the guy is evil incarnate as a businessman but face it, he is doing a lot of good with the money, and pledging to do more....give it up folks, find another target...