A webmaster is a credit force to the success of any website. Sure, there are other persons that play a contributory role, but the webmaster is considered to be more indispensable than the rest. Part of the reason for this is because they deal with the technical aspects of website development. These are not easy to understand without prior training. Authoring in the proper language and scripting using the most desirable formats takes training, and an understanding of all these aspects and more, is something a webmaster is expected to have.
Setting up a website takes more than simply having a host and a catchy name for it. There are so many details that come between having the plan for it, putting the plan into play, developing it, and finally presenting it into a fully accessible site with a reliable server. This middleman task, which, even in writing sounds somewhat complex, is easily done by a website administrator- if they have the right set of skills for it. Any material developed for the site has to be coded in HTML, so it goes without saying that a webmaster has to gain HTML expertise. The language itself is not complicated, but you need to work with it for a long time to truly understand it.
Content management depends on the purpose of the site. A news site or one that regularly needs updating -sometimes several times a day- needs a committed content manager. If the site is commercial, said manager, who is still considered a webmaster as far as job title is concerned, is responsible for running advertising campaigns, marketing, and basically keeping the content of the website accurate and updated. For this, a lot of creativity is needed. Use of SEO as a marketing tool is a desired quality in a content manager, since it has a proven track record of increasing the rank of a website.
A good webmaster is skilled when it comes to the technical parts of web development. A better one can not only attest to having that, but also being creative enough to meet the content management needs of a website. One might argue that stepping into content management oversteps a boundary, since there are content managers with the training to do that. But this is hardly the case. After all, there are content managers who are going into the technical parts of website management so there is basically no argument there. Having both skills, undoubtedly, makes you a more marketable webmaster.