The piano is a good instrument for many uses - classical, traditional, ragtime, jazz. Therefore, using a piano hardly means that a singer is using a dubious accompaniment.
I have a friend who is a piano tuner, and she's involved in an exposition of new composers who call for 'prepared piano,' which involves doing things to the piano. I think putting pillows in was one form.
At which we all rolled our eyes...
I once wanted a snare-drum sound, so I placed uncooked spaghetti in a bodhran. Despite columnists, despite tradition, despite politics, musicians are going to make the music they want.