This quote from Jacqui Cheng says it all:

Long story short, [Frederic] Wolens claims that Facebook is on the verge of fixing up its content systems so that "deleted" photos are really, truly deleted from the CDN within 45 days. But with the process not expected to be finished until a couple months from now—and unfortunately, with a company history of stretching the truth when asked about this topic—we'll have to see it before we believe it.