I'm not sure as I don't belong to any of these but here are some examples (US) that seem like they "work well"... Screen Actors, Directors, Writers all have guilds. Real-estate and Lawyers have decent looking guilds, they just don't call them by name. Doctors, Dentists and Nurses also have guilds (they call them associations).
SAG, DGA, and WGA are all labor unions. The other cases I'll grant you, but it's less clear what their direct benefit to their members is besides acting as lobbying organizations.
SAC, WAG, etc. are all labor unions similar to the one Bandcamp just created. Don't be confused by the name.
--
As for the other examples, what I like about tech is that anyone can join the industry. I think the way attorneys and doctors have set up their profession works for them but it really makes it hard for anyone who didn't choose the golden path to join.
