I have taken my silicone case off a few times since launch and mine still looks new. Could be that some are defective or maybe the way the case some people take them off? I don't pull on the corner but take it off about half way between the bottom and half way point on the case so I don't put pressure on the thinner bottom edge
Possibility. I feel if certain instructions are necessary however they should be provided. Regardless I don't feel corners of mine should be "worn" like they are.