Yamaha have always had separate lines for arrangers and synths, (The arrangers developing from the Electone (Organ)) whereas Roland and Korg arrangers were mainly developed from their synth line, hence the inclusion in their arranger keyboards of some of the sounds from their synth rangers. (The Yamaha arrangers are designed purely for the home market (And if you don�t believe that last comment then just ask Yamaha)
Enjoy whatever you play

Bill