Lu,
All the analysis in the world does not make armor stop what it can't stop. Except for the big Russian machines (Mi-28 and KA-50) the Apache is a lot tougher than anyone else out there. Furthermore, the fact that Apaches and Black Hawks are being downed by RPG's says a lot for the US Army requirements. NOTHING FLYING can withstand an RPG hit in a critical area.
As rjsquerril said above, the lessons of Iraq have little to do with how helos are made, and a lot with how they are being used.