Whilst as a Guitarist I have to agree with this, there is still a lot in a good hardware synth that completely changes and improves the playing experience.
Quality and action of the keys, the way the aftertouch works (or Poly AT like on my Hydra which is a joy to play and has a ribbon ). A one knob per function type interface with great feeling high quality knobs really adds to the experiance...as do wooden end cheeks You do feel the difference with a guitar, but I have still bought a lot of guitars because of the way they look