I think this is to scare the dust away. It's the only reason I can think of why someone would make a case for the PS3 that looks this...creepy. Attaching on top of your existing case (instead of having to replace it), they apparently go for around $15, but why you'd want to spend one dollar, let alone fifteen on something to make your PS3 look like something from Doom 3 faceplanted on it is anyone's guess.

Sony PS3 Protective Mask ideal for Halloween [I4U, via Giz]