- The author correctly points out that Woodrow Wilson essentially changed the format of the address through precedent from written document to speech. Right after Wilson's first speech there is a huge drop in the "education level" (hang on for a discussion of this terminology) of these addresses. As I recall, Wilson is the only American president with a Ph.D.
- The index used - Flesch-Kincaid (FK), is questionable. Good on The Guardian to use a single measure for all speeches, but I have to wonder if it is wise to use the same measure for speeches and written addresses. Furthermore, FK is very sensitive to the placement of punctuation (it weights sentence length heavily). For instance, as a friend pointed out, one of Wilson's speeches has a FK grade level of over 17, but if you replace one of the semi-colons in the speech with a period, the FK grade drops to 12. This subtlety is lost in speech format, giving FK an extremely high uncertainty (this same friend calls FK "utterly useless" for speeches).
- The audience of the SOTU address has changed. Though it's a constitutional duty of the president, the delivery as a speech is not, and it only has to be delivered to Congress. However, most modern addresses have been in the form of televised speeches, and have to be understood by a wider and less politically savvy audience.
- Cultural trends in the use of spoken and written English in America involve shorter sentences over time in general.
- In this case, a more sophisticated natural language processing analysis might reveal some interesting trends. For instance, how do wartime speeches compare to times of peace? Are there any natural categories of speeches that fall out? What are the outliers? How does this compare to polls?
In short, we have some interesting data that needs heavy qualification and critical analysis, that is just presented on a page and capped with a headline that gives an overly simplistic interpretation.