Not great journalism if they can't get The Duchess of Cambridge's or Princess William of Wales title correct. I thought The Fail had some poor reporting.
People magazine actually spent a while trying to decide what they should call her (as The Duchess of Cambridge seems a bit formal and a bit too much for a headline). The even had a poll on their website at one point asking readers how they thought they should refer to her. Since then, they've gone with "Princess Kate." So, in their defense, they know they're wrong, but they decided to be consistent with their incorrectness.