Through the Bungie Weekly Update the developers reveal a little bit of the story and why fans won't be blasting Elites in New Mombasa.
Under new management the Elites are cast as incompetent and so stripped of their rank. The Prophet of Truth, pulling a Chancellor Palpatine, has schemed to further his own power.
"We realize that the Elites are of a fan-favorite, so it's probably wise to set aside your compassion and steel yourself for what is about to come. There are no Elites to fight in Halo 3: ODST," reports Bungie.
"The Elites had exhausted their usefulness" to the remaining Covenant prophet "and he would not place his rightful transcendence into the hands of incompetents."
Clickto read more on why the Brutes are the minion of choice for today's religious zealot.