I always thought that they are quite literally taking chances with these warranties. Perhaps they know from experience how many people actually go through the whole process of submitting a claim. On top of that there should be some qualifiers in the warranty terms that filter out a certain percentage of the claims on the basis of incomplete/wrong application. And what you would have left in the end is just a handful of people with absolutely legitimate claims (and by that point probably quite aggrieved) that makes it easier to simply hand them a couple of cans (buckets even) of paint, no questions about the surface prep asked.
They obviously should be confident about their paint enough to know that it will last at least beyond the point at which most average people would have simply lost their sales receipt. I'd say after the first three years from the date of purchase, probably 90%+ of customers no longer have all the proper paperwork to actually submit the claim.
Anyway, I'm sorry if this came across as too cynical, but my personal opinion is that any extended warranty is more of a business process than a technical or, it the case of paints, chemical one.
We often have representatives and dealers of paint manufacturers visiting this site, perhaps we can have another comment in here based on their specific industry experience with paint warranties.