I think it's a little disingenuous, or perhaps naive, to say that Wired (for example) is faring "worse" because it has a disproportionately high amount of "Intermediate"-level material. I opine that Wired's distribution of Basic/Intermediate/Advanced material is likely exactly where they intend it to be.
Of course, IEEE is going to pack as much meaning and domain terminology as possible because they are talking to a limited audience that speaks their language. Yet those same technical papers could be unpacked and broken down for a wider audience by using laymen terms. It doesn't mean IEEE has smarter people; It just means they speak that vocabulary.
The results in the article are slightly skewed. They are presented with a "space" between "site:" and "domain". For example, "site: plos.org" has advanced at 86% and "site:plos.org" has advanced at 71%. It looks like the difference is the "spaced" form is doing a document term search and the non "spaced" form is doing a site search.
The Spectrum's print edition is exceptional; That being said though, any moderate technologist can read the Spectrum. The Spectrum is not a collection of whitepapers, but a series of articles on broad topics and even investigative reporting that I wish were more mainstream (e.g. Dec. 2009 article on what its like to run an electrical generating station in Gaza). Pretty much any Wired reacher can handle it if they can stand not having a liquor ad on every other page.
Actually, arXiv.org beats out IEEE, only proving what us scientists knew all along :)