you could be on to something in another post someone said that sam was mad and was sending all she had at us, i dno if they were the exact words but it went something along those lines, maybe you have to activate something else, also there are 6 steps to getting death machine and if you look at this from the campiagn mode a few match up but not all,
1. Secure the keys.
2. Ascend from darkness. (Ascension reference or turn on power)
3. Rain fire.
4. Unleash the horde.
5. Skewer the winged beast. (blow up rocket, maybe)
6. Wield a fist of iron. (Acquire the Death Machine.)
7. Raise Hell.
8. Freedom.
back to the matter in hand, if the next step was raise hell then that could link in with samantha "sending all she had, at us" and thats what the death machines are for? who knows
maybe someone else could add to this, oh and [brains]