You know, from the very first day I began reading this site, the Wrangler RT/S's were always stated to be crap. Had me worried for awhile and almost to the point of buying new tires even though mine had <10K on them. When my ST hit ~12K, the cupping became apparent and had me looking for new tires again.
At this point, I rotated the fronts to the rear and installed Rancho RSX shocks all the way around. With additional rotations ~ every 4K, I have not experienced the cupping issue again. At ~20K and with proper inflation, I really don't see a problem with them. They actually look close to new with not much tread wear noticeable. Look like they're going to be good for at least another 30-40K miles.
Yeah, I could probably find a quieter or softer tire but afterall, the ST is a truck with a truck ride. I just can't justify the cost for replacements.
As far as the tread cracking, I haven't experienced it but I'm inclined to agree with Scott. If it worries you, and you are planning on a long distance drive, then go ahead and change them out and be done with your worry.