Korg's relatively more full and "live" sound, Yamaha's detailed and polished CD-like sound...I suppose the beauty behind these differences lies in choice and/or preferences, as well as the player's/entertainer's needs.

Some simply prefer the sound(s) (and styles) of one over the other (some, like John Smies, have both), and both companies are very successful with their own unique product.

It would be boring (and limiting) if all arrangers (and synths) sounded/performed exactly alike.

Ian

PS...It's the same reason we have Mac's and PC's (with many different browsers)...Toyota and Honda...McDonald's and A&W.