e.g. if I search for the hospital and I eventually find it 3 miles down the road from where the map took me, how would Apple/their mapping partners ever know that the POI should be moved?
One possibility is that the phone keeps track of the fact that "you drove 3 miles past where you were 'supposed' to stop, and then stopped at some other (specific) location."
As more and more people do that --- search the hospital, drive past it, and stop at the same specific location != the phone's predicted location --- then, statistically, we can infer that the "specific location" that everyone eventually stops at is, in fact, the location of the actual hospital.
Interestingly, this implies that the current mapping problems will eventually sort themselves out... after annoying a sufficient number of customers!