Soundwise you are right, a single keyboard like G70 or Tyros5 can do it all...

But i dont think there is a Keybed that allows you to do both play piano and organ parts optimally, even the awesome keybed of the G70 is a trade off... As said, i do want a high quallity 88 hammer action piano keybed, with not to light action, and its extremely hard to play fast Organ pieces or glissandos at those..