As one who has been caught by unexpected turbulence in cruise and rolled almost 90 degrees in the process, I can assure you that it gets real hectic just trying to hang onto the aeroplane. The activity in the sharp end is so intense that there really isn't time to say anything to the pax.
I suspect that, in the case you mention, ptarmigan, the Captain undoubtedly gave his apologies just as soon as he could. The whole episode would probably only have lasted a few seconds, though it undoubtedly would've seemed longer. I think you've gotta put that one down to being "just one of the things that happenfrom time to time".
Bear in mind, too, that most airlines include advice in the initial PA from the sharp-end about wearing seatbelts at all times when seated, in the event of unexpected turbulence... or words to that effect.