Most (if not all) Facebook games have unique items and/or bonuses that can be bought with Facebook Cedits. Most of these games have their own form of credits that can be bought with FB Credits or real world cash. An example is "Shiny" used in BYM. A game having its own credit system allows the game company to give out credits as part of the game (again, with BYM, you can pick mushrooms for a chance at 3-8 shiny). Anyway, the point of all this is that it looks like BP is finally getting its own credit system.
Most places that offer a chance to upgrade instantly will show a small FB credit image. However, curretly if you try to change a turret, you'll see a small gold coin with a Draconian symbol on it. This "Draconian Gold" may be the new BP unique currency coming out.
Hmm, I don't recall saying all those things, but that is SO what I would have said.