I've been able to upgrade my development server from 4.0.0 to 4.0.2.1  without applying my web.config file and all content appears as I expect.

However, out of curiosity, I ran the upgraded default web.config against my existing one, and I'm seeing the following difference and I ask the cognoscenti -- is there something I'm missing?

4.0.2.1 has:

 <!-- ASPNETAJAX -->

  <system.web.extensions>

    <scripting>

      <scriptResourceHandler enableCompression="true" enableCaching="true" />

    </scripting>

  </system.web.extensions

4.0.0 has:

  <!-- ASPNETAJAX -->

  <system.webServer>

    <handlers>

      <add name="HTML-Handler for URLrewriting" path="*.html" verb="*" modules="IsapiModule" scriptProcessor="%windir%\Microsoft.NET\Framework\v2.0.50727\aspnet_isapi.dll" resourceType="Unspecified" requireAccess="Script" preCondition="classicMode,runtimeVersionv2.0,bitness32" />

    </handlers>

  </system.webServer>