You can always add thickness (as you point out you did). Those of us that like thinness would be out of luck if Apple made them thicker.Personally, I have never been able to keep a case on my 5. It always felt too bulky.
I'm confident that this is on the device level. I'm not sure how long the data exists on the server, but I doubt it has ever been indefinitely. Apple's servers can't contain all the messages sent by the millions of Messages users around the world.