Risk and Reward in RPGs
The Star Wars RPG is designed around giving your character a huge number of advancement possibilities. It increases the number of attribute advancements that you get from one every four levels to two every four levels. It gives every character more hit points and abandons the old 'vitality points/wound points' system, which makes it less lethal to PCs. Almost everyone gets more feats than before, and class abilities are now 'talents', which provides more flexibility.
The downside to all of this balance and possibility is that it lends itself to a more artificial play style. Your character doesn't need to have weaknesses. They just have a class role, and if they play it well, they know they'll survive and get more shiny abilities. That's not necessarily bad - I wouldn't play WOW if I didn't like that play style some of the time - but it often seems to detract from roleplaying.
Dark Heresy, on the other hand, provides a fair amount of player choice, but also applies some factors that are beyond the players' control. Stats, for instance, are rolled in order, meaning that without some GM mitigation, your character won't be great at everything you'd like. There are random factors in character creation, such as your character's divination, that sometimes provide benefits but sometimes give drawbacks. As the game progresses, there are hazards such as corruption and insanity that can give a character mutations or psychological disorders. And the combat in general is more lethal, with the possibility of permanent harm or death.
The risk and the possible drawbacks sound bad, but they're also a benefit. You don't want your character to have weaknesses, but those weaknesses make them more real, which can mean better roleplaying. You don't want to risk losing your character or having them permanently harmed, but that risk makes your survival and success all the more meaningful.
In the end, I think that both systems are well-tailored to what they're aiming for. It's just interesting to me how, even between two sci-fi RPGs, the aims can be so varied.