This silicone skin is tough and the attached to the sides and ribbing with a tacky feel. All ports, cameras, speakers, buttons etc ... are still propagated to reach. In that regard the silicone sleeve, the E8 does not noticeably thicker - is you feel no difference whether one has with the phone or without envelope in his pocket.
I've owned several HTC phones - the displays were previously always been very robust (although I Wore carry my cell phone in the same pocket as well as the key ring) - it has always been only the body which scored after some time clear signs of use. Therefore, it is in my case not so bad that these cases "only" the housing protects the display and not because I think only the housing needs protection.