One of the big changes that has occurred with the Web is that the author and the publisher have lost control of the layout of the message. On the Web, the reader can alter the size of the text, the font, the colors. They can turn the images off. They can have the whole page read out to them if they want.
The author still has control of the structure of the message: what bits are text, what bits are headings, what bits are headings, what bits are links and so on.
I think that is a really sensible way to set things up. As an author, you cannot predict who will read your message. That means that you don't know if they are old or young, male or female, from Footscray or from France. They might be blind, deaf, color blind or arthritic, for all you know.
So you don't know what people need to do to get your message. They might want the pages all displayed in a huge font. The might need the computer to read to them. They might have changed the color of the text to white on a black background.
All of these changes are changes that affect the layout of the page. The more freedom that you give people to change the layout, the easier it will be for them to receive your message.
If you want to know more about separating structure and layout, the World Wide Web Consortium are developing Cascading Style Sheets, which will help enormously with this problem.
By the way, if you want to be on the cutting edge of Web development, explore the World Wide Web Consortium's site. They are some of the people that are setting the standards for the Web. And international standards represent the real cutting edge.