Nissan dealers at least in this area (San Gabriel Valley, Ca) is trying real hard to fix the problems associated with a newly designed vehicle. Outside of brakes on my 05 LE CC, I've experienced no other problems.
So Nissan is going the extra mile for service fixes...take advantage while you can. A problem like this would be a CP (customer pay) item at Ford, GM, or Dodge with mods.
Well my experiences with Nissan dealership's service departments has always been very good, some of their techs were not hitting home runs, but they tried, and eventually succeeded.
But as Nissan vehicle buyers, we are paying for a 60,000 mile power train warranty. It is not out of the goodness of their hearts that they repair the seals, but out of a contractual obligation. If they didn't do this, many would simply take them to court.
As far as mods, the federal government's Magnuson-Moss Warranty Act clearly states the car manufacturer must prove that the mod caused the issue - an expensive proposition for them to prove this. And what jury would side with the manufacturer anyway. People have been mod'n for decades.
And if Nissan were idiots like apparently [edit: according to you anyway], the big three are, people not wanting to deal with court, would simply wait until the axle drained dry and it would cost Nissan 4x the price of a seal replacement to provide a new axle. It's called a power train warranty and that is what it is.