The 'famous' IG regiments were meant more as examples than the end all to be -ism that they are. Catachans aren't the only bad asses from a death world inspired by the books of Harry Harrison.. just the best known. If players wanted to invent a regiment of their own kick ass jungle fighters from the planet of Booyah, then the Catachans serve as an example of how they could be formed. Same goes for all the other regiments imo.. Armageddon steel legions would be evident on any hive world that has a production of apc's.. or tanks, or whatever..
I always thought this was the better selling point of the game than the fixed chapters, clans and regiments. That anyone can think up whatever they want, find a set of corresponding codex rules that everyone can live with, and battle.
I personally enjoy a themed army that will lose gloriously every time on the battle field, than milking every last point for tactical dice rolling advantages. (I'm also waay too lazy to get to know the rules that well when they get updated every other year..)
My old ork army -that my son has taken command of apparently.., was formed around two big meks who'd become mates during a drinking binge and wandered off to 'build sum shooty stuff'.
Their names; 'Orcrates da Wundah bah', and his trusty drinking pal; 'Plato Sqiggz an' Chipz'. who used to be a rugular Goff lad until he took a spear through the head, which promptly cleared up his head aches, made him want to ponder the universe more often, and help Orcrates tinker on stuff.
The two of them commanded 1500 pts of mad orks, using the old rules where you don't actually command your units, you roll dice for each units prevailing maniacal, deranged or phobia induced behaviour, and hope to Mork and Gork that they do something useful.
Which wasn't often.
