Unable to Remove Web.Config Nodes using Transform

I have a web.config containing rewrite rules like this:

<system.webServer>
    <rewrite>
      <rules><!-- Some rules here --></rules>
    </rewrite>
</system.webServer>

For a particular deployment configuration, I want to remove the <rewrite> node entirely.

I tried doing this:

<system.web>
    <rewrite xdt:Transform="RemoveAll" />
</system.web>    

Based on this documentation:

http://msdn.microsoft.com/en-us/library/dd465326.aspx

but the <rewrite> node remains.

What am I missing?