[bunderbunder]

Also, the "E[foo]" notation is something you'd pick up in an introductory statistics course. Which, IMO, means it's perfectly appropriate to use it without further explanation in this sort of context.

It's not really reasonable to expect technical subjects like this to always be presented in a way that's easily digestible to people who lack any background in the subject area. This article is clearly aimed at people who are studying machine learning, and anyone who is studying machine learning should already have a good command of basic statistics in linear algebra.