Having said that, there are systems that support and promote roleplaying. A great example is GURPS. The GURPS system provides tools that promote roleplaying. The reward system is based purely on how well the player portrayed the character during the adventure. Success or failure at the adventure's goals is irrelavent to this reward.
I'm not picking on you EW, but I have to question this.
Once upon a time, I gave XP for good role-playing. (This was in the dark days of 2e, when you needed huge amounts of XP to gain levels, kill XP was small, and gp=xp was an obscure, optional rule. It threw nothing off to grant bonus XP for roleplaying, snacks, DM bribes, etc). However, I began to notice a certain disconnect between what I viewed as "good" and what my players did.
In particular, I found that how my friends viewed their PCs and how I did differed on more than one occasion. Classically, there were debates on alignment (what I viewed as an evil act my player viewed as coldly neutral) but there were other discrepancies as well (as another example, a cleric of my game had a very different interpretation of "honor" than I did. Where I saw Sir Galahad, he saw Bushido samurai).
Mostly though, I found giving "good role-playing" XP began to equate to "playing in the manner I preferred" on a lot of issues. Thus, players whose styles more closely emulated my own tended to get more XP and thus started to be higher level. After this became apparent, I began giving a flat "good RP" award to everyone, which morphed from "reward for playing in character" to "showing up this week and not derailing gameplay".
Eventually, I dropped the reward entirely. It was so subjective, I began to question my own criteria for judging. Is a player who is an introvert (doesn't talk a lot, but shows up because he likes to be with his friends) being punished? What about someone playing a strong, silent type? Why should I be the one grading my PCs performances?
Since then, I dropped XP for RP and never looked back since. I occasionally grant a small "clever" bonus for very creative play, clever thinking, or outright sheer awesomeness, but the reward is modest and rare. Similarly, there is no penalty for "bad" role-playing, but PCs that are disruptive often get spoken to to promote PC and player unity (and fun).