I don't know about the posters but the idea behind Purgatory is often missed, by both Catholics and non-Catholics. According to the teaching of the Roman Catholic Church, the damned go to hell (okay, we all agree there) but the saved aren't going straight to heaven because they must first pay for the major (mortal) sins that they committed in life, although since confessed and forgiven. That is because it was an offense in the first place an requires compensation to be made, even if it is not for eternity. Also minor (venial) sins that would not keep anyone from heaven in themselves but are still sins are punished in Purgatory, too.
Now, think about that and you can see that almost everyone--according to this view--dies and goes to either hell or something that is like hell but does not last forever: Purgatory. That being the case, even Popes are facing it, which brings us to the appeal for prayers.
If the Pope does not wind up in hell but goes to Purgatory the church has another teaching, which is that the living can shorten the suffering of the deceased in Purgatory by praying for them. Not hell, but Purgatory.
How long anyone stays there, no one knows, but the great saints of the church said that they saw visions in which it was a lonnnnnng time, except of course that we don't think that there is time in the spirit world. So no one really knows.