My Pryme 8 hasn't been causing me any neck pain.

The thing with the foam absorbing the impact is that without something to spread the force out over a larger area, the foam won't absorb much if any of the impact. Foam crushes very easily, when force is focused on it. Expanded foam, like they use in helmets, is even worse, because it tears easily. The thin flexible plastic that most cycling helmets have as an outer skin doesn't have a chance to spread the forces out. The thicker ABS shell of a skate helmet gives the foam its best chance to do its job.