Not sure if they ever did change their minds really, there was always an offer on the table for a discounted rate on replacement springs - and my cost to refurb I imagine was considerably less than the margin they were forfeiting on the replacement offer.
I do sympathise, the paint finish on a suspension spring has a pretty harsh existence - I guess they couldn't afford to set a precedent whereby anyone with a spec of rust on their springs could claim on warranty. They had to assume I'd been abusing the springs somewhat, because nobody else had reported this degree of wear/tear. I've since come into contact with a few people who have suffered similar wear over a similar period of time, and they also bought their suspension at a similar time to me... they just weren't bothered enough to talk to Nitron about it.
If this level of wear had built up over 3-4 years I'd have not made a peep. I think with the best practise in the world a powdercoat finish on a coil spring is not going to last forever... but for the few months I had driven the car, I still maintain my opinion that my springs were not prepped or finished correctly.