I think you could get the same benefit training in Flagstaff, or Boulder, or Mammoth as you could in Iten... IF you had the discipline.
Flagstaff is just as hilly and almost the same elevation, with arguably better weather (except in a few winter months). However, in Iten there is basically nothing to do. No where to go, no car to drive, no distractions. You wake up, run hard, eat, run hard again, then go to sleep. The running is extremely difficult, but the recovery is much better since you're not burdened by running errands, or doing anything at all really. In the middle you have, as Ryan said, extremely good food that is almost impossible to find here. HATC in Iten does it right.
I think Kenyans can come to the USA and train equally as well, mainly because they aren't lured into the distractions (ice cream sundaes, working all day, going to bars at night, etc). In a way, I think Kenyans can go anywhere and train equally as hard, because they have the mindset.. whereas I think it takes a trip to Iten for an American to even discover that mindset, let alone adopt it.