Can someone explain why the latest ring images are smeared on the left and right but not along the centerline?

http://saturn.jpl.nasa.gov/multimedia/imag...iImageID=108481

This seems to be a long exposure narrow angle image with target motion compensation. This method follows a specific point on the rings around Saturn and during the exposure time the rings are "curving" around the planet. This effect is the more prononuced the farther that part of the image is from the tracking point.
By "curving" I mean something of the sort visible in this animation.

I suspect these are long exposure d-ring images.

Yeah, they are. That's definitely the outer part of the D Ring.