One point that I have not seen adequately discussed is the amount of time required for emergency services to respond to the crash. Some have suggested that it seemed to take an inordinately long time. But I believe the video in Post 1819 provides the answer.
San Francisco Boeing 777 Plane Crash - HD 7/6/13 (Part 1) (Actual Crash Footage) - YouTube
You will note that at about 7 seconds from the beginning of the video, the escape slides are deployed. We know that this occurred roughly 90 seconds after the crash. You can see that at about 1:30 into the video, the fire trucks begin to arrive. This suggests a total time of 3 minutes from crash to emergency arrival. Given that the crash took place without warning and at the far end of the runway by threshold 28L, almost 2 miles remote from the nearest fire stations, to me this suggests a pretty immediate response.
See KSFO map at
http://aeronav.faa.gov/d-tpp/1307/00375AD.PDF