But that still works with op casually saying it'll last for a different interpretation of the word "lifetime" than might first be expected, namely a timeframe more closely aligned with the lifetime of the product than the buyer.

Secondly, it seems odd to be pedantic about such a detail when the comment itself already defines the details relevant to the analogy, making it a self-contained statement even if you didn't know what warrantees were. An analogy doesn't have to map 1-to-1 to work, as that's​ what makes it an analogy as opposed to an equivalence. Saying that a dog is as big as a cat doesn't make it a flawed analogy just because the dog doesn't have sharp claws and pointy ears.