TalkLeft will limit commenters to four comments a day if, in its sole discretion, the commenter is a "chatterer," loosely defined as one who both holds opposing views from those expressed by TalkLeft and:

Those who are commenting in support of the position of the defense, in this case, George Zimmerman do not "hold opposing views from those expressed by TalkLeft." Therefore they are not chatterers and the four comment per day thread does not apply to them.

As to the 10 comment day rule for new commenters, you are correct the rule states:

New commenters, i.e, those registered for 30 days or less, may not post more than 10 comments in a 24 hour period.

However, multiple "old" commenters here attacked or criticized the new commenters. Given the number of comments attacking their position, it didn't seem fair to limit their ability to reply to each attack and defend their position.  Otherwise, their view would be drowned out by the those who hold the opposing view. I'm not about to let anti-defense views overtake this site. It would defeat the reason for its existence.

And, you miss the far more important rule:

Name-calling, personal attacks and insults, racist comments or use of profanity by any commenter, whether they are by persons who agree or disagree with the views expressed by TalkLeft will not be tolerated and will result in the deletion of the comment and the banning of the commenter's ISP address, without notice.

The new commenters whose comments I've seen did not respond in kind even when "old commenters" here mocked their position, attacked their intelligence, politics, motives and  more. They responded with substance defending their position. If 20 people attack them, it's unfair to limit their ability to reply.

If there is an objectionable comment, it should be reported to me. I don't spend 24/7 monitoring comments, I check the ones on my threads when I have time, mostly at night.

I also addressed your question here.