I think you might be confusing semantic HTML with the semantic web. (Which is understandable given the mention of semantic tags.)

Using semantic HTML means using <article> rather than yet another <div>. What GP is referring to, however, is adding extra information to your HTML detailing what kind of data is in your tags, e.g.:

    <p vocab="http://schema.org/" typeof="Person">
      <span property="name">Christopher Froome</span> was sponsored by
      <span property="sponsor" typeof="http://schema.org/Organization">
        <a property="url" href="http://www.skysports.com/">Sky</a></span> in the Tour de France.
    </p>

Here, the vocab, typeof and property attributes are used to add semantic information to the HTML. It might also give you an idea of why one might consider that a chore, especially if it doesn't appear to provide any benefit, like making your site accessible to users of screen readers.