Yes, D/C are our most successful pair. But their international success is at a rather minor level. They're not in contention for a World title or even the podium. Best-case scenario probably has them 6th or 7th at Worlds, and that's IF Coughlin is fully recovered. Yes, they would probably place better at Worlds than, say, Scimeca/Knierim. But their placement would not be sufficient to net real gains, such as a medal or a third pairs spot for 2014.
The USFSA usually does not allow petitioning onto the team. The cases when it's occurred have tended to involve very high-profile skaters who were proven contenders at the highest level. Michelle Kwan petitioned onto the team in 2006 as 5-time World champion and 2-time Olympic medalist. Nancy Kerrigan petitioned on in 1994 as an Olympic medalist and two-time World medalist. Belbin & Agosto petitioned on in 2009 as Olympic medalists and three-time World medalists.
D/C obviously do not have any credentials at that level, and their inclusion on the team is unlikely to lead to either a medal or a third pairs spot in 2014. Therefore, I see no reason to allow them on the team ahead of the second-place pair in Omaha, who will have worked hard to earn that silver medal.