The 25-album back catalog of Paul McCartney, which went live on music services such as Napster, Rhapsody, Urge, and Zune Marketplace on Tuesday, has yet to appear on the iTunes Store. In a press release announcing the McCartney deal, Apple said: “Paul McCartney’s full catalog of 25 solo albums will be available for the first time digitally on iTunes later this month.” It is unknown why iTunes has yet to offer the albums — currently,…