Visitor Q said:
That said I generally think it's just tough luck if you get bad stats. The background for DH is a bit of an exception though.
Not just DH, I think. In Deathwatch, or Only War, someone with lousy BS won't be picked as the squad's designated sniper or heavy weapons guy. In Rogue Trader, someone with abysmal Intelligence likely wouldn't rise to Seneschal, in Black Crusade a character with bad Fellowship shouldn't have much success in becoming an Apostate.
The truth is that, more often than not, characters' professions should be defined by their characteristics - barring exceptional cases where a character is ushered into his role based on heritage (such as, say, a Rogue Trader's child following in their father's footsteps). So for true "realism in randomness", we should roll characteristics and then pick the class the results are best suited for. Some players, especially those having difficulty deciding on what they want to play, may prefer this.
Other players, however, come up with a concept long before they roll the dice, and having their creativity be punished by bad rolls may present a problem if the end result undermines realism as well, such as when people begin asking themselves how "someone like that could ever become X" - especially in cases where a character's role would be defined by their aptitude as determined in various tests conducted by whatever organisation is responsible for them.
Still, a degree of randomness prevents "cheese builds" and makes our characters appear more like real people, so personally I believe in the middle ground between having the class determined by characteristics dice rolls and an all-out points buy system. Slight modifications to the end result such as allowing 1-2 results to be swapped and/or rerolled go a long way in increasing the character's viability for whatever job their player intends them for.