"At 200 feet [...] he recognized that the auto-throttles were not maintaining speed and he established a GO-AROUND Attitude."
Actually the NTSB said at that point the PNF "pushed the throttles forward, but the PF already had". She didn't say
how far forward.
How many seconds before impact was this? There's conflicting information about the throttle sequence and timing. One statement said TOGA was not applied until 1.4 sec. pre-impact. Another said throttle was increased 7-8 sec before.
An aerospace consultant interviewed here said had they immediately selected full throttle upon stick shaker activation (about 4 sec pre-impact), they might have made it:
Pilots union criticizes Asiana crash investigation | Reuters
Of course this depends on many factors, including engine spool-up performance, gross weight, temp, density altitude, descent rate, etc.
When the pilots finally noticed the slow speed (presumably at 7-8 sec pre-crash), did they just nudge up the power a bit?