Web 2.0 is used mostly today because it provides great compatibility with most of the browsers.
So that a website can reach maximum audience. That's why the web 2.0 used the div tags rather then the other html standards.
An ASP.NET site also can be build by this standards. Stephen Walther has written great article at msdn with all the knowledge required to build ASP.NET Sites with web 2.0. Here is the link of that article.