Well, OK, think of it this way:
1) Nitrogen will leak less than regular air
2) Nitrogen will be affected less by temperature changes (anyone that has played paintball in the wintertime knows this to be true)
Right? So, using those points, they can then say this:
Once you fill up with Nitrogen to the correct pressure, it will maintain that pressure more regularly. Always being at the correct pressure gives better gas mileage, tire wear, and handling than a tire that is NOT at the correct pressure.
So, while technically there is no difference between a tire filled with Nitrogen @ 32psi and a tire filled with regular air @ 32psi, they can market the benefits of Nigrogen this way due to the side effects of simply not leaking as much.
Ever gotten a chuckle out of ads for weight-loss pills? Fine print always states that they must be combined with a diet and regular exercise. Or is that just funny to me?
This is why I hate marketing departments.