http://wh40k.lexicanum.com/wiki/Imperial_Fists#.UnlbJfku57M exactly. the pen and paper rpg and the videogame are not canon until approved (like the blood raven for expample). but forge world and black library are part of games workshop and are the same entity.
It's what their gene-seed has done since they were created by Games Workshop, it's part of the Gene-Seed a Space Marine receives and has been since very early on, possibly since right from the start. Also, you the same guy from the Elite forums? if so; nice work on the vindicare assassin, I look forward to seeing him in the game.
I'm looking forward to seeing the Dreadknight and how it will be implemented in the Elite mod, thanks for taking the time to help make Dawn of War 2 Retribution, and Elite better with some really nice models.
Don't marines have small forcefield around their heads that they can use when they choose not to wear the helmet?