Because I fear that all the human spam (these are usually on-topic comments) make Mollom less effective.

The example you give does not match the human spam I am talking about. I am talking about comments that add to the discussion, so it's not merely an agree-message.

These are not bulk messages because the content is different. These are targeted messages that I bet Mollom cannot get a lot of information from that is useful.

But I have little understanding of how Mollom works.