V3 dominates because the support is already existing and the interest is already established.  Despite whatever innovation the developer may have put into the figure, it's success is really dependent upon support from other merchants as it demonstrates that a market exists.  Poser merchants have not been willing to risk having a monopolized support for 3rd party figures because they haven't had to.  V3 products sell well enough that they don't have to support other figures in order to make an income in the poser business.

Victoria, in all her incarnations, has succeeded because she is a brand, a la Barbie, J.Lo and the Olsen Twins.  Whether V4, V5, or V99 are compatible with previous versions is irrelevant as the name "Victoria" represents a stable and reliable market.  (This could be where CL/EF has failed in the past by re-naming their figures with every new version of Poser). 

My issue has always been that everyone has to start somewhere.  In the past, there has been a lot of naysayers even before a figure is released to the public.  I just find it interesting that this time it's with V4 and not a 3rd party figure...