Break in is not as much a deal as it was 20-40 years ago. Its more or less an old wives tale left over from the day when you also had to change oil every 3000 miles. Old habits that no longer make sense and traditions die hard, however.
All new vehicles are driven off the assembly line and then onto a train and then off the train to the trailer and off the trailer to the dealers lot mostly by skilled drivers in a hurry. No warm up, just start and stab the throttle. Many get shuffled from storage lot to storage lot. My brand new WK2 had 50 miles on it before it ever got to the dealer. Not jeep, but some high valued cars are extensively test driven for quality control prior to delivery.
The concept of zero miles as a brand new vehicle is old school, but some here take much comfort in it. Today with the more precise manufacturing, driving like you stole it from day one does not affect vehicle life more than taking it easy the first month.
Now you may also find one on the lot that's been test driven a bunch.
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac