Graeme Smith, people insist, is currently playing his 100th Test Match at The Oval. They will not disagree that he is playing his 99th for South Africa, in addition to the solitary "Test" he played for the ICC World XI in 2005. World XIs have caused much disagreement among statisticians. There are those who believe that World XI games played over 5 days should count as Tests, while others believe that they shouldn't.
Two previous World XI series, in England in 1970 and in Australia in 1971-72 were not granted Test status. Had they been granted Test status, Gary Sobers would have ended his career having matched Sir Donald Bradman's 29 Test hundreds, in addition to a World Record Test Aggregate of 8961. He would also have finished with 265 Test wickets, which would have put him joint 2nd in the all-time list (with Lance Gibbs) when he retired in 1974. It would have brought Ian Chappell 4 additional Test hundreds, taking him to 18 and leaving him with more Test hundreds than any of his contemporaries, save Boycott and Gavaskar at the time of his retirement. His batsmanship may have been considered less in the shadow of his brother Greg's.
I don't favor including World XI games as Tests. These games are ad-hoc, involve scratch combinations, and are not played with any predictable periodicity. There is no dearth of Test Cricket otherwise - more Tests are being played today all around the world than at any other time in Test history. As Sidharth Monga points out it is not taking that long for batsmen to play 100 Tests. Mark Waugh took less than 9 years to play 100 Tests. Alistair Cook, who made his Test debut against India on March 1, 2006, is currently playing his 81st Test, only 6 years and 4 months later.
I conclude this post with a two lists. The first invites a comparison of players after the first 100 Tests in which they batted, while the second, invites a comparison of players after the first 100 Tests in which they bowled. Weather permitting, Graeme Smith will join the first list at Headingley.