Playing from Memory - What's the Big Deal?

Yesterday I heard a young string quartet from France, energetic and sincere and all, but severely restricted in their imagination by playing everything from memory.

What kind of memory, I wonder?  It seems to me I heard every beat, every barline, as though they had committed the printed page to memory, not the actual music.  It happens that I knew two of the three works they played in their showcase performance at the CMA conference.  I know the difference between the way they are written down and the way they "go."  These young people clearly cannot afford to know that difference.

That would entail risk-taking; perhaps an inspired sudden change of fingering or bowing, potentially throwing the others off-guard.

But that is exactly what I crave in ensemble playing: that hint of danger, possible only when everyone has access to a printed score to enable rapid reorientation.