Rules are generally made deliberately, but I've known more than one game that was made more fun by an accidental misreading of the rules. When a rule mistake is important enough to spoil a game, or breaks the consistency, one generally notices. I guess it's possible for a game to just be silently slightly less fun than it should be because of a rule mistake, but I haven't seen it happen much. Which possibly says something about the value of complex rules with lots of special cases.
I don't generally find correcting others fun, unless they don't take it well and make a scene about it in which case that can certainly be some delicious schadenfreude. That doesn't happen with the game group, they're generally receptive.
I think the games probably got more fun though. Presumably those rules are there for a reason, and it's not like I'm staring at the rulebook the whole time. I either had a question come up as a part of gameplay the group couldn't answer confidently or something didn't feel right about how the game was playing so I checked and found what I found. On more than one occasion this has led to someone else in the group pointing out some other related element they had found weird until then.