I didn't say anything about allowing roleplaying. I certainly don't think anything that can be roleplayed is an RPG, but I don't see how an RPG could prohibit roleplaying. Without RP, there is just a G.
You said that there is no way to play Deus Ex without roleplaying. As a reply to R.Graves when he said Deus Ex is not a RPG.
About me saying that not all RPGs allow roleplaying. Here's a good example:
Hack and Sash RPGs usually don't allow roleplaying (specially the classics), since you pick a character and all the game has to offer is "kill and kill and kill some more", usually there is not even a proper story or characters background.
Like in the old Gauntlet games, or Chainmail (the combat figurine RPG from where Dungeons and Dragons was born).
Of course, anyone that try enough can roleplay in any game, even in Tetris. Because roleplay is only limited by your imagination, but in the examples I mentioned above, it allows as much roleplaying as the first Super Mario Bros. game. If you try hard enough, you can roleplay that you're the character you're controlling, but the games themselves don't really give any tools to allow it without stretching one's imagination.
About the RP on RPG. It's a different type of "role playing", because there are more than one type.
General roleplaying is different from the specific RPG "role-playing". Roleplaying is when people pretend to be someone or something they are not (which can be applied to pretty much anything). While "role-playing" (as in RPG) is a person assuming the role of a character(s) and deal with the situations using that character's abilities.
In the first you "pretend", in the second you "are". In the first you "play" a role as in an actor in a theater play, on the second you "play" a limited (by the character's abilities) role as in playing a game. Different types of roles and different types of play.
