I value everybody on a certain level, but I care a hell of a lot more about a deep friendship than some brief fling of a friendship.
I suspect it's just because I typically don't get emotionally involved quickly. When I do, it runs deep, but if I've never formed much of an emotional connection, then yes, those people are largely "replaceable."
But I'm not so sure that's a good thing. At least, not across the board.