We're definitely not interested in business success in any sense. In some ways, anti-success is more interesting to us as researchers because academics tend to study communities that are successful, popular, and self-sustaining (like Wikipedia, Twitter, Facebook, etc). That introduces a bunch of funny biases in our understanding of how identity and persistence work in online communities: we've only really studied sites that have pseudonyms or real names and have searchable archives.
To the extent that we do care about "success", it is useful to be able to say "4chan has TONS OF POSTS" because it's a way of saying that the site does, in some sense, work for quite a few people. If it was just a quirky design but wasn't tremendously high traffic (I think the comparison we make in the paper is that /b/ alone has 16 times more daily posts than the 8 biggest news groups on Usenet), it would be a lot harder to get something like this published. People would be more inclined to brush it off and say "well, it's the internet - you can get a few thousand people to use anything." But that kind of traffic is hard to deny. Plus 4chan's role in the web's collective unconscious makes for a great story, too. So bottom line, what researchers choose to study is very strategic, but the metrics that matter definitely aren't about money, but there are lots of other factors.