Think what you will about the relative evil of comic books having variant covers that a comic book retailer has to order X amount of copies of the regular cover to purchase a copy of the variant cover. Whatever you might think about it, it's become a pretty standard sales tactic by Marvel and DC (plus other companies, but DC and Marvel use it extensively).
Marvel has a few incentive covers for Captain America: Reborn #1, one by John Cassaday and one by Joe Quesada.
But get this - the variant covers ship THREE WEEKS after the regular cover.
That's not much of an incentive.
"Order X copies to get this special cover, but then wait three weeks until you get it!" is not much help to retailers.