I've done a lot of turbulence forecasting in my time. It's a pretty big deal in the airline industry. Good turbulence forecasting can mean the a savings on fuel, a smoother ride, and nice experience all around. Relatively speaking, anyway.
Somebody did not get a good turbulence forecast". I'm guessing that the Quantas flight in question was surprised by the turbulence that they ran into. No flight is going to intentional fly into an area of turbulence that will lead to 30 injuries.
Of course, turbulence happens. It's inevitable. That's what the seat belts are for. You just have to hope that the flight attendants don't add to the problem.