I agree, though it's yet another example where small abuses of the medium wind up diminishing it a lot.
It's also a small part of the censorship debate that's heating up now. Where do we draw the line between good vs bad commentary? Subjectivity rules that roost.
I wonder if some form of open moderation where abusive/advertising comments could be zapped out after x complaints would work? The problem there is that politically offensive stuff gets treated the same as simple spam.