Jeff is probably the best person to answer this, because he's the one that came up with the proposal. But, I was the first pro-tem mod on Webmasters and have been with it since the proposal stage, so I'm going to give it a stab. Jeff can chime in if he has a chance, but here it is in a nutshell.
Webmasters was one of our very first sites after we relaunched from the Stack Exchange 1.0 platform to the 2.0 platform - where communities decided what kind of sites we'd create instead of anyone who could afford SE 1.0. One of our oldest criteria that defines a good Q&A site is that it helps you get better at something, something like your job.
Jeff saw a real gap for Q&A for people that maintain web sites for a living - which was Jeff's job at Stack Exchange since the beginning. He wasn't just a programmer, he had to deal with stuff like:
- How to make redirects work properly
- How robots.txt should be set up
- How to deal with SEO scrapers outranking you by using your own content.
- How to make titles more effective for SEO (well, that's part of the above)
There was just no good place to ask these kinds of questions, and since he was a professional (as in it was his job to do this stuff), that's how it was proposed. Running web sites was his job, and he wanted to get better at doing it.
Over the years the site has refined, the community has changed to a degree and the scope has naturally hit a sort of happy medium. Still, from even the first day - we didn't really discriminate based on what your job was - if you asked a great question that fit our topic and scope we answered it.
Names persist, however and there's nothing wrong with still calling it Pro while being inclusive of the broader amateur audience. In fact it helps, because:
- 'Pro' is likely to be more catchy to, well, professionals and
- 'Pro' basically says 'I can find professionals there' which encourages amateurs and enthusiasts to come look for those experts
So while not really applicable in a literal sense, it's still a fine name, at least in my humble opinion :)