ElDragoPazzo
They don't have advance weapondry because it is considered heretical
yep, cause if fluff is to be believed, the dark age was something of a technological rebellion which threw terra into chaos. The emperor was the hero that saved the day, and he destroyed most of the technology.
examples of destroyed technology...
Baneblade and Hell hammer (I think its called) specs. Last remaining baneblades/hell hammers, are on mars.
Advanced plasma and hyperspace technology.
Cure for the common cold (lolz)