Independent approaches and a large number of largely experimental packages is the nature of open source development, yes, and may provide lots of creative new solutions. But to keep a technical language useful and attractive I think it is a very big advantage if there are defined standards, and that people generally favour collaboration over competition in development. This was discussed in the "Tower of Babel <https://groups.google.com/forum/#!searchin/julia-users/tower$20of$20babel%7Csort:relevance/julia-users/EOHKG1pE1uM/c5cCwXj1AgAJ>" thread, which may be what Ben Arthur is referring to? I don't see how that would be achieved by putting them in the same organisation, what is required is coordination and agreement to contribute to a shared standard project.
I can understand if the julia maintainers would require a standard plotting package to be 1) written in Julia and 2) maintained by the larger community. Right now Gadfly fits that bill - the trouble is just that a lot of people (including myself) prefer Plots, which is neither 'pure' julia nor really a community effort, but IMHO a lot more user friendly. (Note though that it is not backend agnostic - it offers a handful of backends, but not others (e.g. Gadfly, Winston etc)). Plots also has the advantage that package developers can offer plotting functionality with Plots without having their package depend on it, which is a potential game changer. I think it can be said that this is still very much in development, and my hope is that over time a standard will emerge that fits users, the core team and package developers alike. I definitely follow this with great interest.
