In an RPG as such, role-playing is the fundamental MEDIUM of the game, just as poker is a card game, and chess is a board-and-pieces game. Without the MEDIUM, you have a different kind of game. Gambling w/o cards, instead using dice,frex, is craps: a dice game. Gambling, as such, is a larger thematic classifier, not a MEDIUM.
It thus makes no sense for players to be rewarded for role-playing, any more than it would make sense to reward poker players for using cards. If you're not role-playing, you're playing a fundamentally different kind of game.
Now, this doesn't mean that you can't play a different kind of game without role-playing; if you give all your chess pieces names and personalities and have them trash-talk each other while playing, you're still playing a board-and-pieces game. You can remove the role-playing and the MEDIUM remains the same. In exactly this way, you can add miniatures to an RPG without fear of changing it into a war game.
Now, how to define "role-playing", well, that's another whole rant...