Kazza,
I don't think your question is stupid at all.
Back in the early days of slash and fanfic, people published fanzines because that is how the stories were distributed. Then the Internet came along and the distribution scheme changed. Suddenly, many more people had access and the whole genre, as a result, has become much more well known.
Copyright law in the US is confusing, to say the least (disclaimer: I do not pretend to be an expert on this!). Probably what Jenna did with SN, or me, for that matter (I had copies of my story (A Love Born From Steel) photocopied and bound to give to friends at the New England gathering last weekend) is a violation of copyright. However, for anything to happen, someone would need to bring a complaint. I sort of doubt that with my 20 little copies of ALBFS floating around out there, any of the friends I gave them to are going to call the copyright police. Still, there is that possibility.
In my experience, the situation I am more familiar with is when a person is giving a presentation at a conference. In the powerpoint, they have a copyrighted cartoon. Someone in the audience of 1000 sees the cartoon, doubts that permission has been obtained, and contacts the copyright holder, who in turn, contacts the violator (in this case, the speaker). Even then, it is relatively minor: usually a royalty is paid, and perhaps a fine, and a promise is made not to do it again.
There are a number of authors (Anne Rice, eg) who have asked that their stories not be used as a basis for fanfiction or slash. Do these people have staff members monitoring fanfiction.net, LiveJournal, and other sites for possible copyright violations? I have no idea.
The other thing that is happening is that where people used to pounce on things, they are becoming less accusatory, realizing that some of these ventures may actually be good publicity. There was a piece on the news recently about NBC and Youtube. Their policy used to be to immediately identify instances of copyright violation (using film that was the property of NBC) and demand that it be removed. They have tempered that stance, somewhat, realizing that many thousands (millions?) of people may see the Youtube video, which is not necessarily a bad thing for NBC.
Leslie