Based on what some have said in the forums, some people are making that. Based on what I've earned, I can see that it would be possible for the person who writes the right kind of Hubs, includes the right kind of additional information (links, pictures, videos, etc.), knows how to optimize with keywords, and generally puts in an informed effort.
There is plenty of information on this site (in the forums and in Hubs) about how to increase the chances of any Hub's earning. Some Hubs earn more than others. The best ones have titles people search for, are unique, offer useful information, and are well written.
People are generally advised, "Don't quit your day job. HubPages is a nice extra income." Although some people manage to earn well when they first sign up as members, most find that it takes a few months to see the earnings start to improve. It can take longer for some than others, but many have found that it takes the first few months to start to earn much of anything, and after that earnings often pick up speed.
Many people share my experience that it took about eight months before earnings started to pick up. (I don't happen to be someone who does much in terms in keywords and other optimization. If I did, and based on what I've been earning, I believe I'd be earning at least the $500 a month. Again, it requires doing that it takes to produce the right kind of Hub, putting in the effort to use keywords correctly, creating a title that people are likely to search for (there are tools that help with that), writing good content, and patience (at least in most cases).