I always looked at any instrument as just a tool, an expressive voice to write with. It even differs from guitar to guitar. Some guitars demand that you play them delicately and really respect the instrument, and some beg to be abused. Same with piano. I know with guitar, I'm intimate with it enough to know when I put my fingers here, it will sound like this. I prefer writing on piano because it's always a surprise.
As quoted in "The PopWatch Interview: St. Vincent's Annie Clark" in PopWatch (11 July 2007)