In the last pic of the transfer case skid plate, the metal bars that are between the skid and your frame are the transfer case drop. That portion of the frame where the skid bolts into the frame rusts on almost every TJ, even on mine which has never been out of Florida and hasnt seen a snow, ice, or salt covered road... ever.
It just looks like it may need to be touched up a bit. not a big deal unless you try and turn one of those bolts and it just spins. Then you have some serious rust