I actually asked the same question a while back. It was because of the "thicker" padding that I was told several parts would not fit my '04. Like the halftop I have since installed and a sound bar. Both of those were designed for the '97-'02s. After removing and throwing away my factory faded padding, installs were a breeze. Bottom line is the "newer" TJs have thicker padding but the diameter of the roll bar is the same-so I was told. Based on my experience I believe that to be true.
Hope this helps