Hmmm. I'm skeptical about the nitrogen tire inflating thing. Here are my thoughts:
1) Regular air is 78% nitrogen, 21% oxygen, and traces of other gasses.
2) Yes, nitrogen molecules are larger than air and therefore less likely to escape, however, each time one adds air to the tire, they're adding 78% nitrogen anyways.
So, let's assume (I am pulling this number out of the "air" for this example) that a tire contains 50 liters of "air" when properly inflated. Given that 78% of the air is nitrogen, then that tire with regular air would have about 39 liters of nitrogen, with most of the balance being oxygen.
Next, let's assume that all of the oxygen escapes between the rubber molecules, and the tire is low. So, pump another 11 liters of regular air in there to bring the tire back up to its recommended pressure, and we'll be putting 11 l * 78% = 8.6 l of nitrogen in to the tire. This added to the already 39 l gives us 47.6 liters of nitrogen in the tire.
Again, after some time, we notice the tire is low, and assume all the oxygen has again leaked out. So we pump it back up, again with regular air, and add another 2.4 liters of air, which includes another 1.9 liters of nitrogen. We're now at 49.5 liters of nitrogen in this tire, which can hold 50 liters of gas in the first place.
After a couple more top-ups, we'd be left with tires that are almost 100% nitrogen, and we didn't have to pay anyone anything.
Obviously, my example is simplified, but I believe the concept is sound.
My $0.02.
Cheers,
Chris