My oversimplified and perhaps flawed view of the pre-Vatican II era (after all, I wasn't even alive during it) is that you didn't do (fill-in-the-blank) because the Church said so. Vatican II tried to offer why, to give reasons for our observances and to emphasize the positive over the negative, as exemplified by the lack of anathemas in the Council documents.
Similarly, Pope John Paul II emphasizes God's love, his mercy, and consistently sees in man a grandeur that comes from a deep faith. I think that this passage from the Pope's Love & Responsibility speaks volumes about how the Church has changed:
For man is a being internally constructed that the promptings of carnal desire do not disappear merely because they are contained by willpower, although superficially they appear to do so; for them to disappear completely a man must know 'why' he is containing them. It may be said that the prohibition is self-justifying: 'why not?' - 'because I must not' - but this does not solve the problem satisfactorily...Only when the will is confronted by a value which fully explains the necessity for containing impulses aroused by carnal desire and sensuality. Only as this value gradually takes possession of the mind and the will does the will become calm and free itself from a characteristic sense of loss.Doesn't our recent history mirror in some micro way the differences of emphasis in the Testaments? Wasn't the OT (and pre-Vatican II) mostly about telling you that you'll do this because...God or the Church said so? And the NT (and the Vatican II documents) reminded us why? (i.e. Love, i.e. Christ, i.e. because God so loved the world that he sent His only son.).
It seems as though a "hard ass" method was employed pre-Vatican II, while a more "here's why" way was employed post-Vatican II. But is it any wonder that the Church struggles with where to draw the line respect to dissident theologians or how strict to make the fasts when, in our own lives, we have so much difficulty determining whether we are too easy on ourselves or too hard? It'll be fascinating to see where we go from here.