well when you smoke it, you still exhale THC. if you where to think of it as smoking one gram or eating one gram, you would obsorbe all the THC from one gram if you ate it, where if you smoke it you would loose THC.... so based on that eating weed will take longer to get out of your system simply becuase there is more thc in you, as opposed to smoking where you loose some.

EDIT: once the thc is in you... its in you, it dosn't matter how it got there, ie. smoking, eating, injecting.. and its stored in your fat cells...