Citi is pursuing an interesting strategy in issuing co-branded cards. They have partnered with one airline (AA), one hotel chain (Hilton), one online travel agency (Expedia), and now one club store (Costco). (I think they also issue cards for some other retailers, such as Macy's, haven't kept track.) This allows them to fully support their partners because they are not also issuing cards for a direct competitor.
Costco is also on an unusual course by accepting VISA in the USA, but MasterCard in Canada. This has the benefit of maintaining a relationship with both networks, but it means consumers who shop cross border may be confused or inconvenienced.