My oppinion is: The add isoparm tool exists because you can't split nurbs, since they aren't small planes. It is the same process with the split poly tool. You can split the plane faces as you like, since they can't become curved. So, adding isoparms is almost the same as splitting polys, the difference is that isoparms are more practical, as they add a loop split to the object. But for polys loop split, grab MJPoly Tools. Hope I'm explainin' all right.