It is actually rather hard to see, even on a larger picture, just how off square the walls are. Can you measure it with a level? I do know the tolerance on bowing of walls is 1/4" on 32" of the length, but that's a different thing - it assumes straight framing, bad drywall. In your case I think you are correct - it may be a framing issue. I am not aware of specific tolerances in this case. This could be an architectural feature for all you and I know at this point (highly unlikely if it simply looks off, I agree). The crack is a problem, and the builder will be happy to fix that, I am sure (because it's easy). While you have them out to asses the crack, do inquire about the straightness of the wall. I would be interested to know what they say. It is nearly impossible to fix at this point. But you may be able to come to some agreement or get compensated. I know a homeowner who had gotten a deck built for him as a compensation for a rather serious foundation related problem. The developer had fixed the foundation and thrown in a deck to keep the guy happy. This is likely not the same scale of an issue, but you may still be entitled to some compensation if they cannot fix what you don't like. I am assuming the house is still on their warranty, so the time to contact them would be right now.
Please post the results here, I an very intrigued by your case. Good luck!
