Buster, if you're obviously in trouble (JL 747 or the BA one that flamed out in the ash cloud) then the pax have a right to know. Shutting one down under ETOPS is not 'trouble' - that's what ETOPS is all about. Had I been in the 777's cabin, I would have thought it unusual to reduce speed in the cruise but not something to be concerned about. Suspect 99% of the pax didn't even notice.