Mass-market paperbacks generally don't use acid-free paper, so that yellowing is simply a natural process as they age (though exposure to sun speeds that up). Eventually your copies of Destiny will do the same.
I don't think they all use the same cover stock or interior paper. Yes they all show signs of aging over time. However only the 2 Avatars seemed to yellow rapidly and there was residue on the interior covers. I understand this was not an isolated incident.
