If you choose this build, you will get a lot of attack speed, that means your W (true dammage) will "go off" more often, then you won't need any full attack dammage items.
Some of you will maybe wonder why i buy Zephyr, the reason why is because of the passive, the cooldown reduction, the movement speed you get, and i love that when playing Vayne, because you are just like running fast around dealing true dmg every second and no one can stop you.