Keep in mind that most products are compatible with a lot of different versions of Poser. Most vendors will  provide shaders that are for rendering with GC of, since officially, GC is only supported by Poser Pro & PP 2010 and not by all of the other versions of Poser.

Then you have the next problem..... products these days do need to be Poser and DS compatible. If someone is using Poser shaders, you loose a good number of sales. I've done a few products that were using Poser shaders and I had 50% less interest for them then usual.

A lot of vendors unfortunatelly, cannot afford to use Poser only features, it will hurt sales too much.

Artwork and 3DToons items, create the perfect place for you toon and other figures!

http://www.renderosity.com/mod/bcs/index.php?vendor=23722

Due to the childish TOS changes, I'm not allowed to link to my other products outside of Rendo anymore :(

Food for thought.....
https://www.youtube.com/watch?v=pYZw0dfLmLk