OBJ is not a NURBS format. It's a polygon format. Normally, if your app supports NURBS formats you don't want to output as polygons and degrade your model.

With MoI you can export as SAT, STEP or IGES. They're all NURBS formats and they will keep your geometry details 100%. Of course not all programs treat all formats same but after a little bit of investigation you'll find the best working exchange format for you.