httpHandlers versus handlers

In Web.config: httpHandlers in system.web is of IIS6 while handlers in system.webServer is of IIS7. http://world.episerver.com/Documentation/Items/Tech-Notes/EPiServer-CMS-5/EPiServer-CMS-5-R2/Changes-Between-IIS6-and-IIS7/ touches on as much.

In system.web one may need to add assembly references likes so:

<assemblies>
   <add assembly="Microsoft.ReportViewer.WebForms, Version=10.0.0.0,
         Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A" />
   <add assembly="Microsoft.ReportViewer.Common, Version=10.0.0.0,
         Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A" />
   <add assembly="Microsoft.Build.Framework, Version=4.0.0.0,
         Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A" />
</assemblies>