The weight listed is for a short motorcycle jacket, if I understand correctly. The coverage would probably just be the torso, and not the arms, if I was guessing. 2.6 pounds isn't that crazy then. I think it should be considered that the lightest items probably aren't the ones with the highest levels of protection, and then it makes more sense. About using nylon, there are lots and lots of types of nylon, it covers a very wide area. People can be too brand-conscious, they hear 'keylar' and go gaa-gaa, but poo-poo nylon. Heck they could make it out of goat-milk spider-silk, materials are one part, what they do with them is the big thing.
It should also be noted that a problem with woven fabrics is that they lose strength because the fibres cross over each other, they get bent and stuff. So the latest versions don't do that, they take layers of strands going one way, and then lay them on top of a film with strands going the other way, and do that over and over. So it really is important what you do with the materials you have.
