Pianists may need different kinds of hearing than what’s needed to play the violin. Because the tuning of pitch doesn’t require constant attentiveness — I’m convinced there are rather good piano players who actually hear very little of what’s happening as they play.
More than other musicians, pianists are likely to intone or moan audibly while playing. It’s pretty conclusive evidence that whatever those players hear is not objective. The physical sounds being produced are less what is being heard than some “idealized” or subjective sense of the music being made.
A lot of piano music is multi-voiced or harmonically complex. I’ve been surprised that even some professional pianists are rather inaccurate listeners. In an audition, a young player flew through Chopin’s Étude, opus 10, no. 2. She omitted the middle notes of many of the three-note chords in the right-hand part. After she left the room, some remarked on the speed and perfection of her playing. When a colleague pointed out that the piece had been simplified by leaving out those middle notes, not everyone agreed that the notes had been omitted.
Pianists play more wrong notes than other musicians. We have a lot more notes to play. Hearing Hepzibah Menuhin play part of Schoenberg’s Suite on television, I was shocked to hear one wrong note she played consistently (it came around the same way in a repeat). Consulting my score, I found it was I who had been misreading! There are examples of recordings by quite well-known pianists where whole passages are read in the wrong clef…
When I have played Ignaz Friedman’s fanciful recordings of Chopin’s mazurkas for other pianists I’ve been surprised by fine players who tried to deny that Friedman added low bass intervals of a fifth that are clearly sounding.
The person with less accurate hearing (or less accurate memory) lives with greater uncertainty in the playing of scripted pieces. It can make for inaccuracy, or that uncertainty can even bring more flexibility, requiring more imagination and more careful attention to the real sound of music vibrating in a room.