When i bought my jeep the other day I signed a "don't use chains" waiver, due to the laws in California (in the sierras at least) we are required to carry chains.
I asked the dealer about this & he informed me that tire "chains" should not be used, but cable type chains are acceptable.
I'm new to the jeep world but been around snow and ice my whole life, the biggest mistake people make about driving on the ice is:
Four wheel drive will get you going just fine on the ice... but it doesn't do anything when you need to stop in a hurry.
I carry chains because of the laws but like someone else said they will probably shut down roads before requiring chains on 4x4's with M+S rated tires.