Hmm.. did some reading... looks like the tire pressure is not the main reason for using Nitrogen in the aircraft tires:
PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES
Sec. 25.733 Tires.
(e) For an airplane with a maximum certificated takeoff weight of more than
75,000 pounds, tires mounted on braked wheels must be inflated with dry
nitrogen or other gases shown to be inert so that the gas mixture in the
tire does not contain oxygen in excess of 5 percent by volume, unless it
can be shown that the tire liner material will not produce a volatile gas
when heated or that means are provided to prevent tire temperatures from reaching unsafe levels.
And some other cons of using O2:
a) Ice formation at high altitudes
b) Dry rotting rubber tubes
c) Oxidation of the magnesium rims
Originally Posted by KIRASIR
Nitrogen is used in airplanes to minimize the variations in tire pressures at different altitudes.