There's a pretty clear idea of what Texas BBQ is, and should be. Personal preference isn't going to make much of an impact because these places are all being judged against that standard.
And regarding the variability issue, the places that make the list, have been tried numerous times by the writer and his staff, to check for consistency. Any place making this list has to have proven it can consistently cook excellent BBQ. And places that are inconsistent but might occasionally be great, aren't going to make the list.
I think the real issue with the rankings, are the politics and the power of the influence. Most people still consider Franklin to be the best, but the list gets more attention if there's some controversy, so they'll rank others above Franklin. And also, they know they can help stimulate business at some of the lesser known places, and I think they rank them higher accordingly. Franklin has a 4-hour line every day anyway, and it's not going to hurt his business to be ranked a little lower. But a high ranking can really influence business at lesser known places.