I guess what I am really alluding to is that I see so many 5 star ratings for these old films than more recent films. So maybe "classic" was the wrong term. Maybe a classic is different from a 5 star rating. For example, if I was a reviewer, I would give City Of God, Amélie or The Kite Runner 5 stars. But I bet they would only get 4 on the Radio Times Website. Where it seems anything old film in black and white automatically gets 5.
Both City of God and Amelie are given five stars in the Radio Times (and rightly so); the other one was only given three, though.
As for older films more likely being given five stars, maybe it's simply because the best films tend to last over the years and that skews the impression that black-and-white films are automatically given higher ratings. There were plenty of bad old films that have been made in the "good ol' days", but they tend to get forgotten or not shown as much. Saying that, I've seen a few examples of old films that have been given one, two or three stars in magazine listings, etc.