All good points but the fact still remains that other than original organ players and piano players, an OMB (especially those who use arrangers) are intentionally, for economic reasons, cutting out other instrumentalist.
Now economics is not the only reason personalities, competency of other musicians, practice times are all other reasons.

But remember when some of you play as an OMB, you are not just using keyboard sounds (piano and organs) bur you are using saxes, trumpets, guitars and bases and drums and other live instruments.
To tie this in with another thread, why do you think the majority of people on this forum have the Tyros 2. Because of the SAV that try to mimic acoustic instruments. And what about the comment the Roland and Ketron have a live sound. So you all are trying to sound like a live band.

Do you think if they were no arrangers there would be no live music?