I'm surprised R is on there but ggplot2 isn't. R is great for working with data, ggplot2 is great for actually visualizing that data. I believe Wickham is considering redesigning ggplot2 to use D3 to enable interactive visualizations.
Regarding ggplot2 and D3, it's already possible to draw ggplot graphics in the browser, consider looking at the following two repositories:
https://github.com/hadley/r2d3 https://github.com/gigamonkey/gg
You'd probably want to speak to Hadley for more information on his goals, regarding ggplot2 & D3. I'd certainly like to try out any combination of these tools.
In my line of work, clients are more concerned about "out-vizzing" the competition by creating mind-blowing "Wow!" vizes. Doesn't this rule ggplot2 out for the most part?
While d3 is a great tool for analysis as well, it's more for presentation than exploration, I think.
R and ggplot2 are for exploration & analysis, with the added benefit that ggplot2 makes wonderful plots fit for publication. They're quite beautiful, and well done, but not creating interactive, shiny visualizations.
They all have their place in the ecosystem.