How come it's not considered a dark comedy?

Having just watched the movie for the first time, I was very impressed by it. But also surprised, because I was expecting a heavy drama, but found myself laughing out loud during several of the awkward situations.

It's a great movie, with great performances and brilliant direction, but this is more along the lines of "Happiness" or "A Serious Man", then , let's say, "Magnolia".

Makes me wonder why it's labeled more like a drama.