I think these tutorials are missing one of the most important parts of D3 if you want to incorporate it into any serious application and that is the "Enter, Update, Exit" process (http://bost.ocks.org/mike/join/). The "update" step is sooooooooooo important in applications that few to no introductory tutorials talks about. If devs are taught about the update step from day 1, writing future visualizations will make much more sense. Otherwise, any update to a chart will just append new nodes to the UI.