Very well said, and all facts! Aircraft have utilized nitrogen filled tires for years for the exact reason you stated. In the KC-10, I've seen Total Air Temperatures in the -50s°C while cruising in the northern latitudes at the higher flight levels. Eventually, everything starts cooling, including the fuel and the nitrogen gas in the tires. Nitrogen simply adds some pressure stability while preventing moisture that would freeze in the tire.
Yes, most vehicles now run pure nitrogen in the tires from the factory now days, however I can't attest to Chrysler's practices. The color of the valve stem caps doesn't necessarily mean anything. Tire/repair facilities will sometimes install the green caps during a tire change indicating the tires are filled/serviced with nitrogen. My Saturn Outlook came filled with nitrogen from the factory with black valve stem caps. When I had the tires replaced and the TPS valves rebuilt at Costco it came back with green caps.
As mentioned, the tires are still subject to gas laws regardless of the gas used to fill the tires. A tire sitting in the sun will heat up and the pressure will rise. Below are some general tire maintenance tips I posted in a previous discussion:
General tire maintenance tips:
-Rotate approximately every 5,000 miles
-Cross non-drive wheels. Move drive wheels straight forward.
-Balance on every rotation. A wheel with a slight imbalance that may not have been noticeable while mounted on the rear will become noticeable when mounted on the front through the steering wheel.
-ALWAYS re-torque aluminum wheels within 50 miles after mounting. This includes those who just took delivery of their new Challenger. Go re-torque them, you'll get about 1/8 of a turn before the torque wrench clicks. Torque settings for your wheels are listed in the owner's manual. Never use lubricant or anti-seize unless specified with the torque specification.
-Never use your EVIC for setting tire pressures. It may take several miles until the sensors send the current tire pressure to the sensor/EVIC.
-Adjust tire pressure for outside temperature. The tire pressure will rise 1 psi for every 12°F outside temperature with air and 1 psi for every 10°F with nitrogen. If you haven't adjusted the pressure since winter, your tires are over-pressurized.
-Adjust tire pressure when cold. If not possible (warm tire), add 5 psi to the factory (door label) pressure setting.
-NEVER set the cold pressure indicated on the tire sidewall. This is the MAX pressure setting to remain within the designed structural limit of the tire. This does not account for the weight of the vehicle. Always set the manufacturer's labelled (door sticker) pressure for proper tire wear and contact patch with the road.
-Do not set tire pressure when tires have been sitting in the sun. The tires will be hot and won't provide accurate readings. Always set the cold pressure when the tires are in the shade during the coolest part of the day.
-Never run directional tires backwards. This may seem like common sense, but I've seen it several times. For proper rotation of directional tires, the two non-drive tires must be dismounted, flipped, and re-mounted during the rotation.
Whether it's air or nitrogen, you'll be fine, regardless of the original gas type in the tire. If they are low, you can add air to a nitrogen filled tire.
For some additional reading, here is more than you ever want to know about nitrogen filled tires:
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=191