Any property placed into a residuary trust is subject to gift tax if during life or estate tax if at death. It does not avoid any taxes. Gates is avoiding taxes because he’s making donations to a 501(c)(3) charitable organization. He gets a charitable donation deduction for whatever he gives away. If he gave his entire $130 billion to the foundation he would pay no gift or estate taxes.
I just remember that Jackie O’s estate was in a charitable remainder trust where the estate grew tax free and the kids got the return on the tax free growth with what was an equivalent to taxing the estate at 3 to 5 percent. Pretty much nothing.