KW actually does mean lifetime. I remember reading it in the manual when I bought mine and I've seen a few guys on e90post go through it. One in particular I remember I think had them for 12-13 years and they honored it but with a catch.
KW's customer service is notoriously horrible. They're slow, difficult to deal with, and it obviously has to be on their terms. You have to remove the suspension from the car, ship them to KW disassembled (no springs, etc.), and wait like 2 months for them to inspect them and get back to you. From there, they'll rebuild/replace fluid, seals, etc. so they dampen like new and ship them back. For the guy in question they actually just sent him a whole new set with springs and everything.
Obviously that's like close to 3 months downtime so he bought a new set, shipped his in for warranty, then sold the new warrantied set they sent him. Huge pain in the butt, but lifetime actually does mean indefinitely by KW's terms. Good luck!