hmm...i guess i'll try to answer these two also....you said that because of the inherent nature of the piano, all pieces will sound the same if played "right". for one thing, there is no way that two pianists can play the same piece exactly the same way because of the limits of human capabilities, and there is no one correct way of playing a particular compostion, but those are just superficial answers. if every pianist had your viewpoint, what would be the reason to play the piano? as i said, each pianists interpretation of a piece should add something styalistically, or pianistically new and creative, no matter how small the contribution is. playing the piano really has nothing to do with the technical make up of the instrument. yes, the tempo, note length and dynamics are certainly defined on paper, but the composer expects pianists to take those notations and mould them by their own craft. despite what many may think, classical music is flexible to an extent, and is not so static that its performers are restrained by what is written on the music. even "strict" composers like bach, mozart and beethoven leave room for interpretation, although the learned pianist should stay within the styalistic period. also, i'm not sure what you mean by saying that pianists can only be creative by making their own variations. do you mean a variation they compose themselves, or a "variation" in terms of interpretation?......from what i think you mean about the second question on vartiations, (pianists or composers who create variations on a theme of a tradtional piece...) i do agree that some "vartiations" are not vital or interesing contributions to the piano repertoire, such as the godowsky-chopin etudes (but thats just my opinion) but others, like, of course, rachmaninoffs many transcriptions or variations and his variations on a theme of paganinni are endlessly imaginitve, and not just a rehashing of more brilliant material, but music of his own personality and temperment. or, if you mean variations like the ones u find within a mozart or haydn sonata, i they are interesting exercises exploring every possible way a theme might be looked at or listened to, or written.
for the second question, the piano is definately not like learning to ride a bike, i tell you this from hard learned experience. i thought that if i learned a piece, even if it was challenging, i'd be able to pick it back up once i was "done with it". that was a wrong and musically immature notion. once you learn a piece, you should think of it as going directly into your repertoire. you should continue to practice and grow with it, it will only get better with time, this way you'll have it forever and be able to play it in your sleep so to speak. you should never try to ressurect or re-learn a piece, or think of it as absolutely finished. that will just back fire when the time comes to dig up that chopin etude or mozart sonata you forgot about. phew.