To those who think the crew should have noticed the lack of acceleration:
I recently flew TG from BKK to SYD in an A340-600 and being a keen SLF observer of all aspects of my flight I was a little worried as the takeoff roll commenced without any appreciable g-force apparent.
However, the flight rotated well within the runway margins and off we flew, admittedly conservatively in the climb department.
Comparing that takeoff sensation to the previous A300 takeoff (moderate g-force) and the Dash8 Q400 departure (significant g-force) I can well understand crews who regularly experience flex takeoffs know better than to rely on apparent acceleration.