I suspect that this is the opposite to the thousand sons, since DG/nurgle players have been coasting (as far as CSM have been able to caost) off +1 T for a long time. That and the usual issue of being the army that gets put in the starter set to be the NPC race against the marine overlords.
Good point - in addition, Death Guard has just as many brand new players as Space Marines, but with fewer die-hards.