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Air is 78% nitrogen. If the "other components" in air did in fact escape more rapidly than nitrogen we would all be running (effectively 99%) nitrogen in our tires after 3 top offs.
We would fill our tire with 78% nitrogen. The pressure would drop as other stuff leaked out to 78% of the previous pressure. When we topped off we'd be at about 96% (I'm calling it 80%, and 80% of the missing 20% is 16%) nitrogen. The other 4% would leak out. When we topped off we'd be at about 99% nitrogen.
Again, regular checks are much more valuable than nitrogen as if this theory is true you get nitrogen anyway.