Vinciane, I assumed you were already aware that the keyboards of real organs-- including (as far as I know) of modern electronic organs such as Hammonds-- are not touch-sensitive, and I wasn't arguing for or against Yamaha's decision to make organ voices respond the way they do (or don't).
Personally, I think it would be nice if this behavior were something that could be switched on or off with each individual voice, rather than a global keyboard setting-- which is apparently overridden at the voice level for certain voices.
For all I know, it might already be possible to control this at the voice level-- certainly it can (I think) be controlled at the voice level on the PSR-S models and above, and it must be possible on the PSR-E models if Yamaha is doing it, although it might as well not be possible if there's no way for users to access this on the PSR-E models.
Even though it wouldn't be "authentic" for organ voices to respond to velocity as most voices do, it might still be interesting to play them that way-- as though they're organ patches on a synthesizer that has touch sensitivity.