Probably because what he is saying in this post doesn't align well with Tufte.

The premise of Tufte, or at least his aesthetic taste, is that graphs should be as information-dense as possible. The premise of Seth's post is that the only point of a graph is to get someone to understand the emotional impact of an idea. So instead of sending someone an email telling them that sales are down 12% this quarter, you show everyone a graph with a thick red line sloping down and to the right.

That isn't a graph, it is a graphic.

Or a "chartoon", as Tufte calls them. http://www.youtube.com/watch?v=YslQ2625TR4

There's a similar emphasis on removing "chart junk." I don't have the books handy to confirm, but I don't think Tufte is entirely about information density, especially because in some cases, there just isn't density available. The case study about the shuttle disaster in one of the books was very much about presenting just the right information and communicating the "emotional impact of an idea."

Or at least his disciple, Stephen Few.

I worked on some dashboard projects and have found that following some basic good guidelines from Few really improved the end results.

As a plus, the Few books were short and simple, so a minimal time investment was well-rewarded.