This appears to be one of the only ways to purchase a digital iTunes giftcard -- the Apple site itself only offers physical versions, and sites like Gifts.com and Giftcards.com don't have them either. Aside from this Facebook app, the only place we're seeing the option is from within the iTunes desktop app itself.
The report notes that the Facebook application's interface was designed by GroupCard, while the back-end is driven by Blackhawk Network, which has a long-standing relationship with Apple and is a prominent player in the gift card processing industry.