> The semantic web as I understood it was just using the right HTML tags.
Using semantic HTML (rather than presentational HMTL) for content is somewhat related to the Semantic Web, but not equivalent to it -- the Semantic Web is/was about open, composable ways of extracting and processing meaning from content on the web. HTML itself (even HTML5 or the current state of the HTML Living Standard) -- even when used in a cleanly semantic way -- isn't expressive enough to do much with that without building additional ontological structure on top of that, hence things like RDF and Microformats.
Using semantic HTML (rather than presentational HMTL) for content is somewhat related to the Semantic Web, but not equivalent to it -- the Semantic Web is/was about open, composable ways of extracting and processing meaning from content on the web. HTML itself (even HTML5 or the current state of the HTML Living Standard) -- even when used in a cleanly semantic way -- isn't expressive enough to do much with that without building additional ontological structure on top of that, hence things like RDF and Microformats.