MSR had a line of climbing and cycling helmets in the 1980s. They offered free replacement of involved helmets. This was both an advertising ploy and an attempt to get feedback on actual performance.
Giro will replace their helmets that are used in an accident.
Giro, Bell and a few other bicycle helmet brands are all owned by the same company (I did some work for them once back in my banker days). They will gladly replace your helmet if it is involved in an accident, providing you send it in to them for study. As a one time avid cyclist, I have a few friends who have taken them up on the offer. I believe the same holds true of most motorcycle helmet brands.
My goal was always to have to pay to replace my helmets at the end of their useful lives!