Apple updated the bumper, I havent seen any threads on this so I am guessing it is pretty new. Things that I have noticed:
Better fit: there is no gap between the phone and the case. With the older model the bumper could be shifted with the phone in the case.
Better rubber not only was it tougher to get the phone in, but the rubber got tighter after the phone was put in and left alone for some time.
Bigger and better plug port. Not only was the hole enlarged for aftermarket plugs, but a piece of plastic was placed inside so there are no scratches on the metal band. This is pretty big since the majority of complaints were about this issue.
Better fit: there is no gap between the phone and the case. With the older model the bumper could be shifted with the phone in the case.
Better rubber not only was it tougher to get the phone in, but the rubber got tighter after the phone was put in and left alone for some time.
Bigger and better plug port. Not only was the hole enlarged for aftermarket plugs, but a piece of plastic was placed inside so there are no scratches on the metal band. This is pretty big since the majority of complaints were about this issue.