An useful device here might be the word "about", LW is framed to be about rationality, so everyone who think they know anything about rationality think they can participate. However, in practice it is about a specific type of rationality (that it happens to be the type that can be considered the only one is for the moment irrelevant) that requires having read the sequences. From an outside view one might even argue that LW is "about" the sequences "rather than" rationality.