Meh. I've aired down Cooper AT3s with good results and will continue to do so. They're just covering their legal butts. I recently emailed them about street pressure on my new E rated AT3 XLTs and they responded with some similar boilerplate and links to the national tire association size/load charts. Which is fine, I can use those charts to calculate my preferred pressures - based on the factory tire size and door pressure, then adjusted for the load rating on the new tire size. How on earth would they even begin to make recommendations for aired down use off road given the myriad variations in load, surface, and equipment? Even if they told me a pressure, I doubt I'd trust it because they don't know the exact situation. Driving off road almost certainly means using products outside their design parameters and you either accept that (and the lack of warranty implied) or leave the vehicle stock, inflate the tires to door pressure, and stay on pavement.
I work in R&D for a company that sells retail consumer products. In today's litigious society we sure as heck aren't going to publicly tell you it's ok to use a product in any way other than what the legally-checked label advises. On some products that are Federally registered, it is actually a federal crime to use a product in a way that is not explicitly described on the label. Now, as the guy that makes the product, I know it's effective to use in a lot of other ways, but I'm not about to tell you to do it. We get frivolous lawsuits on a regular basis even when we take the legally conservative approach.
