I never heard of a lifetime warrantee on water heaters. I wonder how you collect on it 30 years from now? If you buy a water heater at Lowes or Home Depot, they wont let you return it the next day if it doesn't work. You are supposed to call their "technician" and have them come out to fix it.
The way I understand the rating on how long a water heat will last is based on the metal rods used to heat the water. You get better metal for more money, and they give it a longer warrantee.
In my experience with warrantees, if you have a claim, they give you a replacement of what failed. I've had this happen with flooring several times. Also with plumbing fixtures, and lighting fixtures. In every case, the replacement arrives at the clients home, and the company is done with their part of the warrantee. Now the client has to hire somebody like me to replace what failed. With flooring, this is always very expensive!! So far, in every case, they hate the flooring so much that they switch to something else and throw away the brand new warrantee flooring that they got in order to buy something from another manufacturer, or totally different type of flooring.
I've never been involved in a water heater warrantee job. It makes me wonder how that is handled, and who pays for the labor of replacing it?