I wonder about the behavior of HN users. Do they vote up an article for the article, or for the discussion taking place?

Sure the (original) article does not deserve to make it to the top of HN, so why is it up there? Is it being up-voted because of the content of the article, or the content of the discussion, or because commenters have posted in a popular article and want their comment seen/possibly up-modded?

The last case is obviously the least desirable, but what about the other two? What should the community be voting on?