NURBS is something FAR better than polygons. NURBS(Non-uniform rational B-splines) are mathematical curves between points rather than having fixed "lines" been points which is what polygons are. NURBS have infinate detail level when it comes to being converted
E.g you can convert NURBS to whatever resolution of polygons that you like.
Edit: Btw game engines would likely use NURBS if there was enough processing power since it would look so much more awesome