Webpages are, at their core, based on a simple language called HTML (or, in some cases, languages derived from HTML). This supports a very elegant concept, that a page should be, above all, about its content. HTML encodes content information- whether a group of words is a paragraph, or an address, or a header. Unfortunately, many web designers have lost their connection with this concept. In their desire to produce a certain look, they break the underlying structure of the webpage. This is very easy to do with the tools available today: browser scripting, Flash, assorted plugins, and complex tables.
You won't find these things used in your pages. Encoding will be strict XHTML, with content clearly and accurately marked. Your audience will have access to your site no matter what browser they use, no matter what accessibility tools they may use, and no matter what browser extensions they have (or more importantly, have not) enabled. Styling- the elements that give your page its own look- will be where it belongs: in a separate component called a cascading style sheet (CSS). CSS provides a powerful tool to control the appearance of your pages without interfering with their structure.