(1) Apparently the stick shaker did go off a few seconds before impact.

(2) NTSB spokesman indicated that the black box that monitors flight controls shows that just before impact someone in the cockpit hit the thrust levers to try to power out of the situation, and the engines responded normally. She also mentioned in this context, although I'm uncertain of the reason, that the British Airways 777 engines were Rolls Royce, while the Asiana plane was equipped with Pratt and Whitney.