The attack happened because Stevens stiffed the Turkish government. 0bama didn’t send in troops because he was trying to protect those retaliating against Stevens on behalf of 0bama’s BEST Friend, The President of Turkey (Erdogan)!!!.
The first problem I have with this theory (Turkey) over the revenge killing theory (al-Libi) is that why would AQ telegraph it for weeks or even months (chatter + Stevens "need security force" emails).
al-Zawahiri wanted revenge for al-Libi -- and remember al-Libi was a terrorist who specialized in attacking embassies! -- and so they get the "Rahman Brigades" to do it as almost a cut-out, instead of AQSL->LIFG, who you would have expected as the first stringers if it had been a Turk-related arms deal gone bad.
The second problem I have with this theory is that I fully expect Bobo to try and tangle up this whole investigation by flooding the zone with various ideas of inestimable internecine warfare -- remember, they blamed the whole thing on the tape, then Romney -- rather than the truth; and the arms deal lends itself to that kind of palace intrigue, versus the hard-copy truth of the Embassy missives imploring State for enhanced protection, and the subsequent consequences of State's negligence.
How did he stiff the Egyptian?