I don't believe that is true; I post the following simply for clarification
They state
i.e Amsoil will not "rescue an engine" not properly maintained prior to use of Amsoil.
and
i.e One cannot "just run to 25K" (which actually is "up to 25K or 700 hours, 15K for severe service) without suitability validation.
As previously pointed out by Pablo there are reasonable ways to extend OCI to x2 to x4 the mfg recommendations and then there are reckless ways.
I'm guessing the pushing to 25K without a UOA is the latter, not the former, and Amsoil never indicated they would stand behind the product if that were done.
Additionally, they cover losses confirmed by a failure of their product. They don't cover things like roaching a motor due to an oil pump failure because you happened to be running Amsoil, Amsoil's claims and warranty appear to be about as widely misunderstood as the concept of a 5W-30 being "too thin" for starting a car that specs 10W-30