This is the case only if we are planning to be the world-builders of a brand new project. Consider that among the many campaign worlds being developed by the Campaign Builders Guild is a project called CeBeGia. This world has already a significant developement as well as some ideas on the world geography itself.
Not that there aren't adequete world-builders among the membership of the CG, and not that there aren't substantial mappers in the CBG community - its just that we are an alliance of sites and we should be working together in some respects. It seems playing World-Builder among the CG is counter-productive to involving the CBG.
Both projects are similar and yet are treated as mutually exclusive. Besides the CeBeGia project is not without some level of development already and may be ready for mapping by CG members without having to wait or struggle to new developments.
In all sincerity from me, however, I understand the marketing viability of working with a vanilla world - to capture the attention of the widest pool of players and GMs, but I've never played, GM'd or spent any development time on vanilla worlds. I like my icecream with flavor! I would work on any periphery areas of the campaign world that's not completely vanilla. Even if I participated, I'd never play in a vanilla campaign world. For me it would be an exercise in world development, rather than a project fulfilling any personal goals beyond that.