Well, if you have this line in web.config,
<httpErrors existingResponse="Replace" errorMode="Custom"/>
IIS 7 always return follow text no matter what you specify for statusdescription which I belive it is the default IIS description for 410.
"The page you requested was removed."
If you have this line in web.config, IIS returns detailed error message with your statusdescription.
<httpErrors existingResponse="Replace" errorMode="Detailed" />
HTTP Error 410.1 - Gone
The requested resource is no longer available at the server and no forwarding address is known.
Is this meet your requirement?