I think it also has somewhat to do with how comfortable the helmet is. I can tell you that my friends IRH is more comfortable than my old tippary (which actually I loved that style helmet, but I either killed them, or like the last one they were too big. )
But seeing that my parents buy me helmets, and I tend to land on my head or bang my head they now by me the really ugly $30 helmets. Just as safe, but a bit uncomfortable ,and make your head look like a bubble.
I also have a big old velvet helmet that I use for riding greenies or show's and that I have to say is pretty comfortable but I can't remember how much it cost or what brand (it's currently sitting at the lady who I ride for's barn...haha)