Gearbox. It's OK. So you changed the art style of Borderlands. It's well within your rights! You are, after all, the ones making the game. You don't need to fall over yourselves justifying the decision.
Posted on the game's official forums in response to what they must perceive to be an uproar, a statement attempts to explain the change as a natural progression. That games never look like their concept art.
[We have]developed technology and techniques to render the concept art look for the game in real time 3d. We don't know what to call the result. You can use whatever term you like. We decided to use the term Concept Art Style.
"Concept Art Style"? It's cel-shaded. And Gearbox: it's cool. This isn't 2003. You can render your game in whatever art style you want, and so long as the game is good, people will dig it. Prince of Persia looked great, people loved it. Crackdown looked great, people loved it. And Borderlands looks great.
We'd rather worry about how the game plays after so long tucked away than how it looks...
Expecting More? [Borderlands]