His piano could make it easier to do certain things — trills came off
effortlessly, the pedaling was smooth and faultless. But the action was so light that at times it was difficult to maintain control of fast passagework, much as with feather-touch power-steering on a car...I tried in vain to simulate the sonority of his mighty octaves; it would not come. The piano could not magically correct wrong notes, insufficiently flexible fingers or a lax foot on the pedal.
Obviously, Horowitz took most of his sound to the grave.
Yes, at the end of the day, it's the pianist and not the instrument that wins the day. Sure helps to play a fine one, though.
Link (Via Arts and Letters Daily)