I'm surprised noone commented on the "as a percentage of my income" bait. So I'll bite :)
It is in no way obvious or written in stone that what matters are "percent of income". For many centuries, per capita tax was the norm. Indeed, you could argue that what matters is the actual, absolute amount taken from an individual, by threat of force, and not some abstract proxy metric. There, arguably, Buffet delivers more than you?
The amount delivered without the threat of force (charity) is yet another thing.
For several thousand years people where taxed by land owned which was effectively an income tax. It was hard to guess how much income someone had because they could always hide some of the harvest but if you farmed 10 acres or 10,000 you still paid at the same rate.
It is in no way obvious or written in stone that what matters are "percent of income". For many centuries, per capita tax was the norm. Indeed, you could argue that what matters is the actual, absolute amount taken from an individual, by threat of force, and not some abstract proxy metric. There, arguably, Buffet delivers more than you?
The amount delivered without the threat of force (charity) is yet another thing.