Yeah, I know they can produce a higher SPL in the ear.
What I was trying to say was that with canalphones' sound isolation, users don't need as high a SPL to listen to music compared to headphones without sound isolation, leading to less hearing loss with "normal" usage.
If the user pumps the volume up as high as it can go for his "normal" usage, then yeah, canalphones will definitely screw him over.