DrIstvaan: +1 rep for mentioning "philosophical time" :-).
My take on this is that spamming (if we take it as making an unnecessary number of posts) goes inherently against "talking about useful stuff". If someone makes many posts, but they all (or at least their majority) have insigthful content, it's not spamming.
However, someone may spam the boards with an overflowing number of posts of varying content in the hopes that some of them will be deemed insigthful and thus be high-rated by other members.
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Weclock: yeah, BUT only one of those posts goes towards rep, so it doesn't encourage an unnecessary number of posts

DrIstvaan: I didn't mean the +1 rep you get automatically every day you post, but that somone may post a lot of things, among which much useless stuff, hoping some of those posts will win the favor of some members who will high-rate those posts.