Everything in this post is consonant with typical music theory.
The most popular chords are the good old I, IV, and V, and the next most popular are their relative minors (C -> am, G -> em, F -> dm).
The example they give of chords following "em" is also pretty much what you'd expect. The most classic resolution for "em" would be "am" (it's dominant -> tonic in the relative minor key).
The more popular resolution here ("em" to "F") is more of a pop music thing, because it's harder to do classical voice leading with it -- classical composers tended to avoid parallel fifths.
Edited to add: Why mention classical rules at all in a post about pop music? Because there's not much new under the sun -- you'd be hard pressed to find any harmony in pop music that Mozart or even Bach wouldn't recognize.
Good points. Many rules in popular music come directly from classical music (after all, it's been around for a while).
However, as you can see in the Hooktheory database, there are many progressions that seem to be unique to popular music.
You mentioned iii->IV, which is a no-no in classical music due to the parallel fifths (more common: V/vi -> IV). But also look at progressions like: C G Bb F, which is extremely common in pop. Here we have a double plagal cadence set up by the dominant that was never used by Bach or Mozart, which is probably best functionalized as: I V IV/IV IV
The most popular chords are the good old I, IV, and V, and the next most popular are their relative minors (C -> am, G -> em, F -> dm).
The example they give of chords following "em" is also pretty much what you'd expect. The most classic resolution for "em" would be "am" (it's dominant -> tonic in the relative minor key).
The more popular resolution here ("em" to "F") is more of a pop music thing, because it's harder to do classical voice leading with it -- classical composers tended to avoid parallel fifths.
Edited to add: Why mention classical rules at all in a post about pop music? Because there's not much new under the sun -- you'd be hard pressed to find any harmony in pop music that Mozart or even Bach wouldn't recognize.