I'm not sure there has ever been a game that has really explained RPing very well. It would be hard to blame the earliest incarnations of RPGs since they were in uncharted waters, but certainly major RPGs of all stripes since then (late Seventies onward, perhaps) all have a hand in not helping codify what happens at many, many RPG game tables. In the past, RPing was learned not from the books but from whoever happened to be at the table where you were gaming. I'm not sure that's enough, particularly when so many new players come to RPGs through the major offerings on the market.
Besides, clearly I want more folks on the lawn and often invite them directly.