Melancholia is a realistic "what-if" science fiction, set in roughly the time we live in. The whole plot is centered around the concept of a planet approaching Earth. Being what it is, why would they choose to ignore the effects of gravity as the planet approaches?
The moon is a relatively small satellite and is quite far from the Earth, but still it makes a noticeable difference to the tide. Now, think of a big planet approaching...
If you stop for a second and really consider the effect it would have on Earth's gravity. It would probably have freed up a whole lot of Earth's mass on the side that it was approaching, such that the surface of our planet and much more beneath would have been ejected from the atmosphere and drawn to the approaching planet. Or, in the very least, gravity would have greatly decreased.
So, how come they didn't even explore a grand finale where the characters are ejected?
I found it terribly unrealistic. Was it a choice of saving on special effects? Didn't the people involved in production even consider the physics of it? Are there interviews done with them surrounding this issue? Or, is it a non-issue as far as entertainment is concerned (i.e. it's not relevant in this movie/genre)?