Let's see: since 2001, Tim Duncan has played in 20 playoff series against a wide array of opponents presenting just about every conceivable defensive approach. In that time, he's averaged at least 20 ppg in 18 of the 20 series. In the 2 in which he didn't get 20 ppg, he had a first round series against Phoenix where he shot 52% from the field and averaged 5.2 apg while scoring 18.7 ppg; in the other, in the First Round against Sacramento last year, he averaged 18.3 ppg while hitting at a 61% clip from the floor while playing only 33 mpg.
For the record, he's averaged at least 24 ppg in 11 of those 20 series.
He's shot over .500 from the field in 11 of those series, including the last two series this year, in which he's shot better than 57% from the floor and both series in 2006 (61% and 56%). He's had exactly 1 series in the last 20 in which he shot less than 45% from the floor -- the 2005 Finals. Of course, he played that series on a sprained ankle and had to deal with Ben Wallace and Rasheed Wallace. And, oh by the way, Duncan's team still managed to win that series.
It might be that Cleveland can do an unprecedented job of controlling Tim Duncan in the 2007 Finals -- but it would be just that: unprecedented.