While it’s true that your epic destiny allows you to bend, break, or ignore some of the laws of the universe, an epic destiny isn’t merely about acquiring even more power. [It is is more about] defining your place in the universe. Your epic destiny is the mythic archetype your character aspires to achieve. Once you reach 21st level, the greatness you always knew you were destined for is no longer theoretical; it is actual.
Head over to DDI to see the complete (though unformatted) archmage epic destiny.