I know a bit about this. I WAS running the same tires as you on my F350. The tires came with a 70K warranty and I only got about 35 out of them. Discount Tires gave me rebate on the difference of my actual miles vs the warranty miles. Enough to drop my cost $123 on each tire.
Michelin is aware their warranty is overstated. Because of this, Michelin has stopped production of the LTX M/S 2 tires and will not be making them anymore. They have been replaced by Defender LTX M/S with a 50,000 mile tread life warranty. They both have virtually identical tread patterns. Despite the Defender having a lower tread life, they have modified the rubber compound to make it wear longer that the 70,000 mile warranty LTX M/S 2.
So as of 2 weeks ago, I now have the Defender and you wouldn't know the difference by looking at them. I would swear that the rubber is a little harder and the tires don't grip as much. Could be my imagination, but they did make the rubber compound longer lasting after all.