I thought the reason for delaying selling of stocks is to avoid capital gains tax, not income tax.
I did a quick google, and most sources seem to support that taxes are due at RSU vesting time, e.g.
> With RSUs, you are taxed when the shares are delivered, which is almost always at vesting. Your taxable income is the market value of the shares at vesting.
https://www.schwab.com/public/eac/resources/articles/rsu_fac...
Why would this be different for the salaries of rich people? Isn't it more that they usually get large amounts of stocks at low prices if they stick with the company for a long time?