I find his writing to be very readable as well. However, I consider myself highly educated, with excellent English skills, and I have been following his writing for some years now.

I was deferring to experts in the field of readability, and considered it likely that they would provide a better measure than self-reports of "looks fine to me."

Further, it seems likely to me that Eliezer is very good at targeting his audience and maintaining interest despite the complexity of his prose. Academic doesn't mean "boring" by necessity. One of the references from the Gunning Fog page states:

Although we have often given permission for reprinting the Fog Index, our means of measuring reading difficulty, we have sometimes cringed at the use made of it. In our work, we emphasize that the Fog Index is a tool, not a rule. It is a warning system, not a formula for writing. Testing without the support of analysis based on experience can be detrimental.

And yes, I do realize that this criticism can be applied to my own use of the tool, but point out that the measure directly supports my initial statement: "Use longer sentences and bigger words," with the caveat that you should also be a good writer, to ensure the complexity doesn't hinder the message. Or I could add, only do this if you can get away with it (still be a successful communicator).

I'd also like to point out that this feels like a good example of the dojo-style response to my clumsy use of a single word: academic.