[63corvette]

First, I am not for it or against it but it is the make up of the air we breathe is the big difference.
Its the moisture in the air that makes the pressure go up and down radically with heat or cooling in the tires.
With nitrogen there is almost no moisture as to bottle the Nitrogen it has been cooled to liquid which requires cooling it to if I remember correctly about -190 degrees C therefore there is basically no moisture in it.
Bottled nitrogen is made from air because there is so much in the air we breathe.
Helium is much more expensive and much lighter which would make it less stable with temp changes. It also leaks out much easier.
Just My 2 Cents