The domain industry as a whole may seem fairly small, but in reality, there are quite a number of people working within it. Not all of these people actually work with domain names, but the industry employs a significant number of people.
At domain registrars, there are account managers, programmers/technicians, designers, executives, and other positions. At domain brokerages, there are brokers, marketing managers, financial managers, and more. Parking companies have account mangers, programmers, technicians, and other employees. There are independent domain brokers and consultants as well, and I am sure I am missing some jobs as well.
Even domain forums have employees. In my opinion, the worst possible job in the domain business has to be a forum moderator. These people probably don’t get paid much, but they have to deal with annoying, whining, screaming (well, written screaming), and general nastiness that goes their way. Some likely have to be on the forum more than they ever would want if they weren’t a moderator. I can’t imagine the pay is good either.
If you are an active participant on a domain forum, you should do your best to be nice to these people. They don’t get much compensation for doing a job that most people would despise, and they can be helpful to you if need something (like a sales thread deleted).