Fans and retailers alike have been complaining about the number of ads in both DC and Marvel's books over the last couple months. Now I'm not generally one to take sides in the "DC vs. Marvel" debate (they both have their share of strengths and faults), but it's been accepted wisdom in the retailer community that Marvel is less retailer-friendly. That's not *always* the case (Marvel did get FOC before DC did), but it's generally true. And here's an example.
DC and Marvel have both overloaded their books with ads for the last couple months, with weighty extra pages and even (in DC's case) bound-in 3D glasses. Retailers pay for that increased weight with freight costs, but don't see extra profits from it. DC has now begun issuing freight credits for their overly heavy books... Marvel hasn't.