While ignorance of the rules isn't an excuse, its far more excusable than someone who knows they are breaking rules but continues to do so.
From my point of view, both ignorance of the rules and continually breaking the rules are basically the same.
Users who didn't care about the rules for one bit should never be allowed to post after all (maybe this is too extreme?).
I agree that accidental rules breaking should not be treated the same as someone who breaks the rules intentionally.
But if someone ignores the rules continously, then they are basically don't care a bit about the forum.
I see a lot of this behavior on my local board. It is clearly stated that they must read the pinned thread. Even if you are new to the forum, it so easy for you to see that guidance thread after all. But sadly, they just don't care as long as they can increase their post count for the signature campaign they've joined. The irony is, not only newbies do that. Even a Sr. Member did.
Are they different from someone who keeps breaking the rules? I don't think so.
Oh of course, I mean someone who broke a rule once or twice in a single occurrence that did it genuinely by accident will not be punished as hardly as someone who is trying to avoid being caught (some exceptions apply). Once you've done it once and you now know, the warnings are over. Frankly speaking, there are a lot of people who haven't read the rules, and some of them are just fine. Basically, as long as you aren't spamming or doing anything illegal, the moderation staff will never pay you any mind. There are a few small rules here and there that may not be 100% common sense like many of the anti spam rules are, like deleting your old bumps and such, but we do keep in mind that some rules are easily missed, and give more reminders than bans about them.