D/S is the gate for poser content into Bryce.

Carrara takes runtimes now so really it can function on it's own without Daz Studio. Carrara 6 imports Daz scene files and Poser pz3's now. Really you could say that Carrara is stand alone because it can do it all by itself.

The reason some still use Poser 4 is because there are still people out there that own and run a Windows 98 computer. Or simply they like it and don't feel the need to purchase an upgrade. Could be why they still use Windows 98. Part of it is that everyone cannot own nice powerful computers.