There are inevitable commercial aspects: there is no such thing as complete safety, only a probability of success (or failure); grounding every 777 in the world (I believe 6-700 are flying now) might not produce a justifiable increase in flight safety, just major inconvenience and financial loss to airlines and their customers.
A lot of the 'experts' being interviewed on TV after the crash said that if there was any doubt about the 777's safety then it would have been grounded. But that isn't really true...I mean for a long time the FAA didn't ground the DC10 despite early problems (admittedly they did ground them eventually for a short period) and arguably the 737 should have been grounded after two instances of rudder hard over. So there could be a fault lurking in that plane....the engines are meant to be completely independent.