i've posed this question to many engineers (even a few who are drummers) and i'm still without an answer. what's even more befuddling is that i have a few recordings where the drums are panned to the player's perspective and it sounds fine (and even more authentic) to me.
Well, I don't know for sure, but I wonder if the statement is even correct.
How often do you see a piano where the player face the audience? In most cases people encounter real pianos (ie at home) the piano faces the wall and the player has his/her back to the audience. In concert situations the pianist usually sits with his side to the audience, so there is no distinctive "panning" at all.
So people "know" that the bass is to the left on a piano, because that's how they usually hear/see it in real life. Plus, most people has plonked on a piano at some time. While few people has played the drums, and mostly see drumsets in rock/jazz settings, with the drummer facing the crowd, hence people "know" that the hi-hat should be to the right, and the tom to the left, even if it's the other way around for the drummer.
So I'd claim that both drums and pianos are usually panned to the listeners perspective.
I pan drums to drummer perspective unless I'm doing FoH or DVD's (even multichannel mixing). I'm a drummer and I do believe that instruments should be in listening perspective before anything.
Now, most of the times this is not my decision. If the producer wants to have listener perspective, he go it! but in a gig, if you have drummer perspective, I find it a bit weird to get used to.
Lennart is right when says that people are more used to listener perspective as drums are rare to encounter BUT I don't think there is a rule. I don't think we should consider a rule. For cymbals like rides and other speciallity (like the bendy Paste one, etc.) I might consider the whole perspective issue to better fix them in the mix.