I interpret the first sentence to mean that a water heater with a 6-year warranty actually died when it reached 6 years old.

I've heard that is not uncommon with water heaters (end of warranty -> sudden death) - unlike the one in my previous house that had a "property of CL&P" (CT Light & Power) sticker on it with a date about 25 years prior to the date I bought the house - and it survived my 14-year tenure. I was told that no one wants to pay what that sort of longevity costs nowadays, but I don't know if that's the issue or not.