I for one am very happy to see this thread. I had a feeling that this "ribbed effect" that I've noticed on some of the newer sterns was just par for the course, but I'd always wondered quietly if some of my playfields had come from a rushed batch or something of that ilk.
Seems as though this is rather commonplace, so for those who have chimed in on this thread, I appreciate it as it gives me closure on that, so my sincere thanks again.