Typical tire fill and in gas struts in landing gear on aircraft is nitrogen, not argon. And reason is no water in production of nitrogen for fill up cylinders and maybe less dangerous if tires catch fire from heavy braking compared to when you just take compressed air for fillups. Also oxygen from compressed air could possibly do some corrosion in landing gear struts, 20 percent in athmosphere is oxygen, rest nitrogen anyway. But then, I wouldn´t care for that bit anyway. I think somebody said nitrogen had a bigger head than oxygen so the tire in the inner tube keeps its pressure a bit longer - possibly. But then, this is not worth the hassle for getting nitrogen and I use compressed air at all times.
Vic