A mesh is a mesh and bitmaps are bitmaps. People have remarked that items don't support Poser specific features - some vendors may not have the time/expertise/desire to do justice to both. Perhaps it's an opportunity for more people to sell stuff to specific markets. In this case, if Dreamlight were to go DS only, maybe some Poser guru could make a deal with them to provide Poser versions of their products with high quality shaders and lighting.

It's been nice to have compatibility, but as the programs become more sophisticated and people demand that products utilize those advanced features, I wouldn't be surprised if some vendors go with one or the other. Personally, I'd contact them and ask about a Poser version before assuming anything. Even if they didn't want to do a Poser version, they might consider about selling a mesh and texture only version at a reduced price. That would work in a lot of applications without requiring export from DS. 

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken