NURBS - Non-uniform rational B-spline
NURBS modeling may look better in a rendering than an ArchiCAD model of the same thing because of how much smoother the curves can be. If your model has no complex curvilinear shapes then it may not be noticeable.
Beveling the edges of things is one of the noticeble things you can do to imporve a photorealistic rendeing. This is not an easy thing to do with an ArchiCAD model. Not so hard to do with the nurbs modelers. Rendeing engines like Maxwell can take care of that. Rendeing engines that can work with displacement maps will help you turn your work in to art.
And then there is the post rendering work. Some people are so skilled with this craft that they can take even a crude rendeing and make it look like it spent all day at a render farm.
on another topic. Have you see the new autograss from vray?
http://www.vray.com/autograss/media/autograss_for_vray_2.png
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