My girlfriend and I were talking about this the other day, and we came to the conclusion it was likely a marketing ploy for tire shops to make money. The air is 78% N anyway, what is another 28% (of the 78%) going to benefit me?
I like the top-off every time you refill your tires. After my average of 75Kmi, I should, by that theory, be close to 98% nitrogen
Daniel