I recently saw Year of the Dog and also had an opportunity to hear Mike White talk about the film. There's a review on Slate, here, that describes this film as "classifies as a comedy only by the slimmest of margins"... "because it's suffused with a deep and incurable melancholy".
Something I never got and completely disagree with is this strange popular opinion that anything called a comedy has to have a laugh a minute, otherwise it's a failure. I read advice here to that effect. Someone will post a comedy script and get feedback that it's not funny because they weren't laughing every five minutes. This is an absurd requirement.
There are plenty of comedies, especially dark comedy, that have quite a range and mix of serious and comedic content.
Then every person has their own definition of what's funny. No film plays exactly the same to every person or audience. Even in a theater the same film gets laughs on certain lines some nights and on completely different lines on other nights.The best comedy is comedy that is written and played straight. I saw Clay Pigeons the other night. In one scene Janeane Garofalo, playing an FBI agent walks into a crime scene and notices the local deputy has screwed up. She hears the sheriff call him Barney, and says, "You're deputy's name is Barney?" That was a very straight line, but I thought it was the most hilarious line I ever heard. This is dark comedy. But, the concept applies to all comedy. You wouldn't think off hand that a story about a serial killer would be very funny. But, it can very well be.