Why is Cinema 4D not represented here?

The same could be said for Mudbox, or Zbrush.
This is primarily a mechanical CAD based website, but people would love to see products and designs made in the more artistic, sculpting programs.

Steve,
I've never used Cinema 4D, but it and similar programs like zbrush, mudbox, maya, modo, 3DS Max, and others are not really used to design the files from which objects are manufactured via traditional mass production methods.

Those programs are excellent and amazing tools for concepts, rendering, graphics and other applications, but sending a Cinema 4D file to a CNC, or injection molding shop is going to be more difficult than sending the same design via another program like solidworks, catia, pro-e, inventor, or any of the other programs which this site has a focus on.

I love the output the more artistic modeling programs can generate. I'd even go so far as to say it/they are the future of much computer aided design.
They just need better precision, and a way of exporting good files which can be read, modified, and used for mass production.

I believe the answer for mechanical design and even industrial design, where specific critical dimensions must be met, is an amalgam approach of parametric modeling and subdivision manipulation. Basically replacing tried and true solid model/surface model hybrid approaches where the skill gap often leads to a compromised design effort. It's a really quick way of going from idea to conceptual model, to final product.

If you want to see some of this in action, this is a good representation of the process: https://www.youtube.com/watch?v=7kIVhxyDHsQ

As FredSWUG said, polygon models have their place but I have to agree... I don't see a purely polygonal system being of much use in the design-to-manufacture world that most of us work in.

I have to agree with the others answers. This is more of a parametric design collection of software, vs programs that basically create artwork in 3D. Not that C4D is not a 3D CAD program worthy of great designs, its just more tailored for TV animation or 3D objects instead of manufacturing an fabrication.