Why is fbx better than obj and what about dynamic importing?

I learned early on that importing fbx models results pretty much in the results I expect but find now that I need to start importing models at runtime and have a problem…

I only see obj runtime importer which would I guess work apart from every time I manually import an obj file the resultant model id very bitty with sections of the material missing, but importing manually the equivalent fbx it appears perfect.

So why is this the case and does anyone import fbx at runtime?

I think there is no fbx runtime importer, I could be wrong but I remember looking for it and finding only negative answers.

The alternative could be AssetBundle but it requires Pro version ( EDIT : no longer in Unity5).

EDIT: Creating a FBX parser is not complicated just really long. There are some available outside of Unity scope which would require to use Process class with parameters.