FWIW I don't consider 20 A/B/H/J that bad of a seat. If row 21 is fully booked (which seems to be frequently these days) I usually select row 20 as a back-up. I would much rather be in row 20 than a non-emergency exit row. Therefore, I am thankful they consider these as Preferred Plus. I do agree that it probably has this distinction because it's an Exit Row which I think many people equate to being better regardless of the actual configuration.