It's because of the rake of the windshield, on most other vehicles the rock is propelled over the glass, but Wrangler's windshield is too brick like. :-P
My 2007 had it's fair share of glass repairs. When I bought my Colorado, the dealer threw in Crystal Fusion treatment, and got the same for my 2012 Wrangler. Even if you have to pay for the treatment, it pays for itself after the first windshield replacement(if you figure OEM glass & labor).