When world-class artists come to the NPR studio, a place with high end upright and grand pianos, to perform; many of them bring Nords Korgs or Rolands. Why do you think that is?
We are not talking about the same kind of piano here. And different artists value different things or just need other features, and the "authenticity" of an upright piano is very likely what they are looking for, which is totally fine. This really is another topic. Sorry.
