Being a world class Artist, means world class Travel. There is simply no choice in the matter if you are on the concert stage. That means hours and hours of time spent flying and in hotel lobbies, or hotel rooms, without access to a piano. Simply to much time to waste. Many times the maestro has gotten you a copy of the score on how he intends to conduct. You really need to be prepared before the first rehearsal , or in some cases a private meeting with the Maestro. Also , no matter how full your repertoire there are new pieces that are presented to you all the time . It is just not practical given that the day has only 24 hours that you can spend enough actual time at the piano to deal with all your obligations and music you encounter. Much of it by need must be done in your head. I couldnt imagine how you could possible be on that level as a pianist and not have a wonderfully developed ear. When I was a young girl studying at Moscow Conservatory with Professor Sofronitsky all students where expected to be able to hear a score in there head. Hopefully that gives a little perspective to this subject. Hopes to all that your musical voice in your mind improves. Lady Pianist.
Relative pitch means hearing the differences between notes. Good relative pitch means hearing the intervals with some precision.