Reverse proxy versus shifting webserver to DMZ

[barcajax () gmail com]

Client=>Reverse proxy (DMZ)=>Webserver (internal)
Is a reverse proxy really that advantageous over hardening a webserver and shifting it to the DMZ? I read a manual from 
a vendor that states the use of a reverse proxy hides the internal addressing. I disagree with this statement as the 
firewall does that function. The way I see it... a reverse proxy (that is built on a different OS from the webserver) 
prevents direct attacks on the webserver. However if the application is vulnerable, attackers can still compromise the 
backend by targeting its application flaws. It is possible to escalate privileges that way. This defeats the purpose of 
deploying a reverse proxy wouldn't it?