That right there is a lie. You -can- dispell with your dice, which is one reason that Tomb Kings can't stand up well against heavy magic armies...because their magic phase just gets shut down.
all TK spells are bound spells and follow the same rule as bound spells. you can use dispell dice to dispell them if you reach the power level of the bound spell or dispell scrolls to automatically dispell them
Pg 34 of the Tomb Kings army book under 'Using Nehekharan Incantations'. It makes it quite clear how the incantations work. They even use phrases such as '...the spell is always cast unless dispelled...' which seems pretty clear right there.