Yeah 95% or more will need a tuning fork at a minimum to give a frame of reference. It is fairly common for strings accompanied by a piano to ask for a note from the piano to start from (G for violin say)
In the case of ensembles with a piano, I've heard it's because you can't retune the piano in the minutes before the performance. So it makes no sense for musicians to tune to a fork (or using an electric tuner) and leave the piano out of tune, so they all take the key tone from the piano