I'm not sure about this, I'm going from memory on it, but if I do recall correctly, the first Otterbox did have a guarantee. But only that first model of the Otterbox had that guarantee. If you read the current warranty policy for Otterbox, note that last clause.

They are explicit and vehement about going after those who would fraudulently present warranty claims. They didn't need to include the emphasis (text in all caps) nor did they need to threaten with legal action, but they chose to include that. Why? Because, and again this is assuming that I'm remembering things correctly, they went through a ton of claims with that first model Otterbox.

The prevailing opinion of most customers is that Otterbox will replace your phone if it's damaged while in a properly installed Otterbox case. This hasn't been true for a long time. Back when I was still working as a corporate trainer in a call center, I had to correct my students on numerous occasions about this opinion.