Why do Catholics teach that Catholics go to hell if they die in a state of mortal sin, but teach some Protestants may go to Purgatory/Heaven?

I have heard, according to Roman Catholic professors and dogma, that if we die with a mortal sin on our soul we will go to hell. However, didn't Pope Benedict XVI say that Protestants can achieve heaven? Most Protestants will never receive Reconciliation, so doesn't this imply that those who have mortal sin can still achieve heaven?