Back in the day, cough, cough, when I crewed on a Super Modified crew, the justification for the use of nitrogen was that it was bottled and therefore "dry". Air with moisture in it would expand at different rates depending on how much moisture happened to be in the compressed air used in the tires, changing the way your stagger would increase or decrease based on the tires temp. If I recall correctly, N2, is an inert gas. If it's free what the heck. If they charge so much as a penny tell'em no thanks.
The shop I'm in now has air dried by cooling, desicant filters and centrifical driers. Over kill if you ask me, just more maintenance problems. Good grief it's not like that air is used in any control system. My tools lasted forever with daily oiling and the occasional Ingersall Rand grease.