Because they have been served a load, i mean glass, of... 
Why would you need a case? There isn’t a problem....
Thank you for finally admitting that.
I don't have a problem. Some small minority of iPhone users in weak signal areas do, and a case will solve that problem.
I however, like most iPhone users, have always kept my iPhones in a case to protect them from accidental damage. Therefor, I will accept Apple's offer of a free Griffin case to provide that protection.
Because they have been served a load, i mean glass, of...