This lifetime memory warranty is for memory purchased after-market from Dell.  The warranty is handled by a separate warranty division when the system itself is out of warranty (or replaceable by Tech Support if the system is in warranty).
Today memory module died on our PowerEdge 2970 system. System is few month out of warranty. But when I started to look for memory replacement, I found that with memory upgrades Dell provide "Limited Lifetime Warranty". The memory which came with our PowerEdge, is it also covered by lifetime warranty, even if server itself isn't covered by warranty anymore?  Or this warranty comes only with separately purchased memory modules?
Lifetime memory warranty and out-of warranty PowerEdge system