It will come as a surprise to no one that I have some pet peeves when it comes to discussing the history of RPG rules, particularly the rules of Dungeons & Dragons. One of the biggest ones usually manifests itself like this: I'll start talking about a certain rule, say weapon vs. armor class adjustment, and I'll express some bafflement as to how the rule was supposed to work or why it was presented in the fashion it was. In reply, my interlocutor will say simply, "We always ignored that rule," as if that answers my questions.
Now, I expect that, in any given RPG, there are large numbers of rules that get ignored, for a wide variety of reasons, from ignorance to laziness to outright disagreement about the utility of the rule in question. I don't have any problem with this fact, speaking as someone who's ignored more than his fair share of RPG rules over the years. My beef is more with the notion that, because a given rule is easily ignorable and likely was ignored by a lot of gamers that it's not worth discussing or trying to figure out why it was included in the game and what the designer hoped to achieve by doing so.
A related peeve of mine pertains to the so-called "Rule Zero." I have no clue where this term first originated, but I suspect it's a fairly recent coinage. According to popular usage, it refers to the supreme authority of the referee to change anything he wishes in his campaign, including the game rules. Now, I don't have any particular problem with Rule Zero as such; I question why it's necessary to codify it at all, let alone in such a goofy way (I am unhappily reminded of Asimov's "Zeroth" Law of Robotics). What bugs me about it is the way that it too is often used to short circuit discussions of odd rules in RPGs. Say I want to talk about the rather low demihuman level limits in OD&D and what its implications for the implied setting of the game and my interlocutor replies, "Well, the LBBs were only intended as a framework to be changed as the referee desires, so I don't think you can draw any conclusions from the way the rules were written." I think it's possible to admit the first clause of that reply without conceding to the second; otherwise, one wonders why any rules were needed at all.
I enjoy delving into the whys and wherefores of game rules. I hold the possibly ridiculous notion that rules aren't included in a game "just because." They're all there for a reason, even -- perhaps especially -- bad rules. Understanding why they're there is not only interesting in its own right, but it also provides firmer ground on which to modify or reject existing rules. That's why I can get worked up when I hear, "We always ignored that rule" or "The referee can change it, so why worry about it?" Call it a weakness of mine, but there it is.