Another factor here may be that G is apparently getting quite good at showing results where the title and page body rank strongly for synonyms of the primary search terms. I've gotten visitors to well-focused pages who did not search for a term that appears in the title or on the page, but rather searched for synonyms of those words -- and even for words that are frequently mistaken for synonyms of those words.
We first saw this several years ago with stemming, but now it's apparently been extended further to synonyms and even to these "quasi-synonyms."
Therefore if the primary search term is centered in the title, but a synonym or quasi-synonym appears prior to it, the "centered-keyword effect" being discussed here could instead be a "synonym effect."
This theory may not apply to the case at hand here, particularly because it says nothing about the reported "demotion" of keyword-on-the-left, but it's something to look out for as a possible complicating factor of the analysis.