Hi Rich_Art - yeah it's because OBJ files usually contain polygon mesh geometry which is a totally different way to structure 3D objects than the NURBS geometry that MoI is focused on working with.

MoI can export to polygons in OBJ format, which it does by taking large spline surfaces and dicing them up into little facet pieces. But it is not easy to start with a whole lot of little diced up pieces and then try to form large truly smooth surfaces out of those.

See here for some previous discussion:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4421.6

- Michael