caste system - check
use political intregues and back stabbing to gain higher levels of status - check
murder/assassination a common way to go up the ranks - check
honor (or at least the perception of such) a huge thing in the society - check
time honored tradtions of combat and arena fighting to prove ones worth - check
the more skilled warrior you are the more you are praised, and get women - check
You have a 'number one' or whatever that guys title is (idential equivlant to klingons from noble houses forget their title however) - check
Oh thats right noble houses who all come together to form the policital body with a king (or klingon high chalancier) - check
While their empire is in decline they are spending all their resources with infighting and backstabbing - check
Sounds like you described a good chunk of human history.
Given that the evolution of Klingons has always in some way mirrored historical cultures and civilizations (from totalitarian regimes to tribal-esque warrior race), it's not surprising that the source material is similar. The similarities you depicted could just as easily make references to the various Indo-European cultures that employed a Caste system. I'm guessing much of what has influenced the current culture of Klingons, was used to influence the creation of Dragon Age's dwarves.
Given the rest of the game sports civilizations that seem inspired by dark ages Europe, it seemed to me that the Dwarves continued the same thing. Caste systems with honor and military acumen being highly valued are common in history. Houses having leaders? Might as well accuse it of ripping off Dune. The Dwarves do seem awfully Harkkonen, now that I think about it. Though perhaps less outright evil.
The Klingon culture isn't simply made up. The only good argument you really have is probably the political infighting and arena fighting.
EDIT: Haha, I swear that I had not seen the other Dune reference prior to posting this.