I believe this is a bug. There are at least two users in the "penalty box" who are able to continue posting comments. See this thread: How do you get your account suspended with comments from Rich B and Welbog.
Considering the two users in question were put in the box for comments in the first place, this should definitely be corrected.
Suspended accounts are dropped to a rep-value of 1, which is the required reputation to post comments according to the MetaSO-FAQ.
As suggested by others, if you are suspended for abusing comments, perhaps you should be suspended from posting additional comments as well. "By-design bug" maybe?
1Good catch. IIRC, SO requires 50 or so rep to post comments. They probably didn't bother blocking the comment feature since the rep drop would take care of that.– user27414Aug 27, 2009 at 19:52
@Jon Yeah, I was thinking of reputation in context of SO, which confused me initially. Had to check here.– SampsonAug 27, 2009 at 19:53
4The penalty box rep ought to be 0 on meta in that case. Aug 27, 2009 at 19:55
1@tvanfosson True. Probably an oversight when implementing Meta.– SampsonAug 27, 2009 at 20:17
The Penalty Box blog post mentions only restricting the posting of questions and answers, so perhaps is by design.
If a moderator has warned you several times via email about behavior, and that behavior continues, for a period of 2 to 7 days, your account will be in timed suspension.
Your account will be locked at 1 reputation.
Your user page will have a visual indication that you are in timed suspension, and for how long.
You will be unable to ask or answer questions.
3Ahh. Perhaps this is more of a feature request, then. It seems like account-suspension should extend to comments as well (especially when it's comments that lead to the suspension!)– user27414Aug 27, 2009 at 19:48
@Jon B: That could be interpreted as having different suspension modes, depending on the behaviour that gets someone put in the box. I would disagree with that, only one suspension mode is needed. But you're right, that should include comments.– TrebAug 27, 2009 at 19:54