It is difficult (and inappropriate) to comment about the particulars of this incident as I don't know anything about it other than what I have read in the newspaper.
It is worthwhile to remember that most airlines with any significant amount of flight operations have severe turbulence encounters from time to time during which crews and passengers unfortunately suffer injuries and sometimes even death. The real problem is that turbulence areas, strength and duration are nearly impossible to forecast, especially for flight deck crews. I don't know whether the aircraft was in IMC at the time or whether the radar plays a factor, but it is valid to keep in mind that CAT is a major hazard to.
I recall reading around this season last year of two separate severe turbulence encounters in the same area (over the South China Sea, in fact) involving a China Airlines 747 and some other carrier. In both incidents, there were injuries to passengers and crew.
Besides the challenge of us on the flight deck forecasting the strength and location of turbulence, another problem is that cabin crews and passengers have become jaded to the seat belt sign going on during flight or do not appreciate the potential consequences. Most passengers and crews have (fortunately) never personally experienced the wrath of severe or extreme turbulence.
But some of this attitude towards the seatbelt is conditioned. How many crews have you flown with who either forget to turn the seat belt sign off or just leave it on for hours, exceeding personal physiological limitations of passengers who after a while just have to head to the toilet? Soon afterwards the sign becomes meaningless. I know the sign also becomes a losing battle for those on the flight deck. Seemingly, as soon as we turn the sign on the air becomes smooth, and as soon as we turn it off it becomes bumpy again.
In any case, the original intent of the message was to express concern for our colleagues and passengers with the hopes that those hurt will make a quick and full recovery. There is definately room for technology to improve the tools we have to work with to provide accurate, real-time forecasts of turbulence.