Not necessarily.  The estate tax (and gift tax) are taxes on the transfer of property.  It is entirely separate from the income tax.  We can have a discussion on the merits or fairness of a tax on the transfer of property, but it really should be a separate discussion from income tax, which is a tax on earnings and profits.  And accumulated wealth that is a result of growth in value or appreciation can entirely escape income taxation when passed to a succeeding generation because of the rules relating to step ups in basis.