My sympathies to all crew including 'tarti' who have suffered from turbulence. The problem HERE is in definition. Turbulence is graded 'light'/'moderate'/severe' so that it can be reported by one aircraft to another. This has NOTHING to do with the perception of the c/crew or passengers.
It is quite possible for trolleys and crew to be thrown around in 'moderate' turbulence. The whole thing has to be a liaison between pilots and c/crew, and ultimately the decision on what service to conduct is down to the senior crew member.
Of course, if this whole Virgin thing was caused by UNEXPECTED turbulence, there is not much that any pilots can do about it - because it is 'unexpected'.
Over 80% of the time when I have a met forecast of 'turbulence' it does not occur. Around 40% of the time when there is NONE forecast it does. It is all a constant balance - if it is 'forecast' over a 3 hour period of the flight and the Captain puts on the signs as a precaution - and thereby suspends service of hot drinks at least - and there is NO turbulence, everyone whinges. Perhaps the answer (c/crew cheering, I hear) is to leave the signs on all the flight. Passengers then move around at their own risk and have no claim against the airline for injury if they are not strapped in.