Before I continue, I need to say that I don't have an opinion about quality of el.pianos sounds on PSR -simply because I didn't used and "studied" them much.
When we try to replicate sound of electronic instruments of famous songs, we should keep in mind, that these artists are using custom voices (many times created just for particular song). And second, song is (heavily) post-processed after recording.
El.piano isn't acoustic instrument: it's sound is artificial and so we can't really say how it should sound. What I'm saying is, el.piano on PSR doesn't necessary sounds "bad" -it just sounds different. On arranger keyboard, we can customize el.piano voice to certain degree only and that's the reason why custom voices (actual sound samples) exist.
Don't get me wrong, I'm not "defending" PSR. We should just accept the fact that, no matter what's the name of certain built-in voice, all these voices are generic: sounds like a Fender guitar or sounds like Hammond organ, etc.
Bogdan