Normally I don’t make fourstrands my personal facebook page, but this thread came up, and I really liked it. Give it a read:
http://www.lounge.belloflostsouls.net/showthread.php?53617-Why-Don-t-They-Put-Their-Helmets-Onhttp://www.lounge.belloflostsouls.net/showthread.php?53617-Why-Don-t-They-Put-Their-Helmets-On
A great piece on the culture of the Imperium.