There is not much doubt that the cabin crew did a great job with the evacuation but the PRIMARY reason for this and a lack of injuries was the very fortunate fact that due to the gear being retracted, the doors were very very close to the ground, you could basically just walk off the 777 before it exploded.What a stroke of luck, which got EK off the casualty hook.Peter.
The other major factor for survivability seems to be the robustness of the 777 airframe. In three major accidents (LHR, SFO, DXB) the airframe remained intact long enough for all the passengers to evacuate. The evacuation slides do, however, seem suspect. They failed to properly deploy in SFO as well as here.