As I said above, 2D plots were rewritten in Maple 11 (Standard GUI), but 3D plots were not. The 3D rewrite was done in Maple 13, which you are clearly using.
Postscript is essentially a 2D format, and drawing 3D plots to it is always going to have a few problems and involve some compromise. One of the compromises we have to make is between drawing surfaces correctly and drawing sharp lines. Most users of 3D plots are drawing surfaces, and we accordingly optimized for that. Surfaces look substantially better than they did. Unfortunately a side-effect is that pure-line plots have the slightly blurry effect you see.
You can reduce the effect by making the plot much larger - as large as you can - before exporting it. That will make the underlying bitmap (what is actually being exported to postscript) denser and reduce the blur.
I hope that's helpful.
David Clayworth Maplesoft GUI Developer