Lifetime of what you bought? That's kind of stupid. Lifetime of the purchaser? If they die the next day, is the warranty void? If you bought a new roof, would it be for the lifetime of the house? Lifetime of humanity?
It means for the utility life of the product. If most can openers last three years and you tried to get a new one based on a lifetime warranty when yours failed after 16 years of service, not gonna happen.
When the wording is "free replacements for life" that means the life of the buyer and those warranties are not always transferable.
This is a question I've had for a long time. I'm glad you asked. It seems like a ploy of false reassurance. If the product dies within the week you purchase it, does that mean the lifetime guarantee is null and void? Too bad for you?! It's not your fault you bought a lemon or the company went out of business. How are you to know?
I'm glad all the people before me knew more than I. Their answers gave me some insight to beware and remember to fill out the warranty cards and send them in.