Content and Structure
When creating XHTML is important for defining the structure. the <tag> helps build the document with the conent that you need to have to be properly laid out. The CSS is the structure of how everything you coded is laid out on the page with fonts, color, boxes.
Time Flies
The world of technology is always changing along with coding. The way things were coded before looked like <td><span class>. Now we have CSS and many more options to include things into that document the label every last detail into the first code. Devices are always changing though with many various sizes so company are trying to keep up with these changes with their codes making it alot of work.