They haven't shown that they are for real already? They have the best record in baseball and the BP's Playoff Odds have them at a 91.7% chance of making the playoffs. I don't think Chicago has the pitching to knock them off this year, unless they make some sort of deal at the deadline.
The main concern I'd have if I were the Tigers is that the pitching staff is a potential house of cards. The team is relying a lot on Verlander and Zumaya, who haven't pitched full big league seasons, as well as Rogers and Jones who could literally fall apart any moment. There are some OBP issues in the lineup, but it really hasn't hurt the offense much.
Detroit hasn't proven yet to most fans that they can and will win a postseason series or three. There have been many teams that dominated during the regular season and then crashed and burned in the playoffs. The 116 win Mariners and 13/14 of the Braves record setting run squads come to mind