There are many element make the web 2.0
EX:
- Using css in HTML Source, mean Use "Div" and Tabless
- Use size of text larger (not sure for all site)
- Use the Big Heading --> Strong to say: Here my heading
- Url Friendly (For Searh Engine Optimization)
- And more....
Here is like a web 2.0 styles
http://lamweb.biz