Well, don't forget, Hammer... arrangers aren't STRICTLY for live use only. Many players (myself included) use them for record production, songwriting, etc. - non-realtime use that a demo of how good you CAN make an arranger, with sufficient time and editing skills, comes in very valuable. And don't feel slighted... the demos for EVERYTHING, WS's included, involve editing unless specifically indicated.
And while, yes, there might not be many on this forum that could approach those T3 demos, I am sure that Volcken, Baartmans and maybe a few others could come SO close, you would be hard pressed to tell the difference. Bottom line is, they ARE using no other gear to make the demos. If we can't come close to what Yamaha's demonstrators do, whose fault is that?
It is still 95% player, no matter what the ad copy says!