I'm struggling a little with how to word this comment. The straightforward way is "If people off oDesk are paying Americans $150 an hour for iOS development, and people on oDesk are paying Americans $30 an hour for iOS development, then American iOS developers should probably not source clients on oDesk."
Odesk and the others aren't a good indicator of the average hourly rate for this sort of work.
Someone charging a freelance rate of $30/hour in north america for iOS work is either not invested much in learning the platform in-depth and therefore won't be able to do much more than populate table views and wire up transitions, or they'll tackle a complicated project at that rate and make a mess for someone else to clean up.
Wake up and smell the coffee .. this is about what the rest of the world pays for programming hours, and it should be so: programming is overpaid in the US.