http://www.aspnetpro.com/newsletterarticle/2005/11/asp200511de_l/asp200511de_l.asp
"ASP.NET 2.0 defaults to XHTML 1.1, but you can also opt for XHTML 1.0
Strict or Transitional. The rendering engine of some controls has been
reworked to make them produce compliant output. As a result, in ASP.NET 2.0,
each control's markup includes a closing tag. Furthermore, the viewstate
hidden field comes surrounded by a <div> tag and the form is only identified
by the ID attribute."
Sounds like they did this for a reason.
Greg