I would like to add something more to my previous posting and say that playing an arranger keyboard is very different from playing an acoustic piano because implies a greater degree of understanding of music composition. With an arranger you are in control of a real orchestra, large or small, and the final result will depend on how you utilize your "sidemen". In other words, when you play a piano you are responsible just for that instrument; when you play an organ you are responsible for the organ and the bass too (if you use the pedals or the bass lower manual); when you play a synthesizer using a brass or a string sound, you are responsible for the brass or the string section and you have to phrase your notes the way a real brass or string section would. And the same goes if you take a solo with a woodwind sound: you cannot phrase the notes on a saxophone the way you would on a piano!
With the arranger, you are responsible for all these parts...plus the drum part! True, you don't play your drums live, but it's up to you to choose a good rhytm (style) and to trigger your fills or your variations at the right time.
It is true that, like any other instrument, an arranger can be played at different levels of proficiency and I agree that the "one finger chord mode" is not the best way to impress those "professional musicians" that look down on arranger players, but the same feature is a blessing for someone who otherwise could never play a keyboard and, thus, entertain his family or his friends.
I am afraid that the arranger image is still tainted from the old Casio days and the association with an "oompa" kind of rhytm, but I am convinced that being able to master an arranger keyboard is a real art, and personally I think that we are only at the beginning of the arranger era.
(So cheer up folks, on this board we are shaping the future of the music industry and of the music business too)