I was thinking this too - the Xperia Z, like other Xperias, ships with a pre-fitted screen protector. I'd like one for the back too though, to keep it looking pristine.
Nexus 5 - Paranoid Android 4 Beta
Sony Xperia Tablet Z [SGP312] - OmniROM
Brought into the light by my old HTC Desire S with Flinny's CM10