The capital gains tax rate is not 15%. It is 20%, plus a 3.8% Obamacare tax. So Bill Gates is probably paying 23.8% on investment profits.

Here in California there is a lovely 13.3% tax, bringing the total to 37.1%. Bill Gates is a resident of Washington, though, so he doesn't pay that.

You can't blame Washington for not having a state income tax, though. Their tax laws seem to have worked out very well for them in attracting companies like Microsoft and Amazon.