Well, as a classically trained musician, I certainly would expect V-I to be much more common than IV-I, as a cadence. (Defining "classical music" as music roughly from 1650-1900ish). But it sounds like the author didn't really limit his analysis to cadences. My impression was that he just counted every chord that precedes a C chord, which even in classical music would include lots of non-cadential IV chords moving to I chords in the interior of phrases. For non-cadential chord progressions, I'd expect IV-I to be fairly common, though it's unclear to me that it'd be more common than V-I. I mean, just the coda of any Beethoven symphony alone would probably skew the stats in favor of V-I, generally. ;) So, I'd like to see the author clarify that.
As for the explanation, I thought it might have something to do with rock's origins in 12-bar blues (I-VI-I-V-I), though I know that pop has moved away from that considerably.
What you briefly explain what you mean by cadential chord transitions versus non-cadential chord transitions? Is a cadential chord transition one that resolves an entire progression rather than merely appearing in the middle of a progression?
Yeah, basically. A cadence is a harmonic progression at the end of a phrase. In classical music it's usually V-I. Sometimes you'll hear IV-I (plagal, aka "amen" cadence), but it's actually fairly rare outside of church music. However, internally, within a phrase of music, you might see IV-I more often. A fairly common example: I-IV-I-V-I.
As for the explanation, I thought it might have something to do with rock's origins in 12-bar blues (I-VI-I-V-I), though I know that pop has moved away from that considerably.