For these reasons:
1) They have some poorly performing ex-Reds off their roster like Fleepy and LaRue while adding two guys with a quality, professional approach, who are great in the clubhouse: Berkman and Theriot. What was evident about the Cards last year is that they played well against good teams and lousy against bad teams. This is symptom of bad approach/clubhouse which the Cards seem to have dealt with.
2) Theriot is an improvement over Ryan--Ryan was too young, pushing limited ability in a lineup that was struggling. Not a good combo.
3) They have tremendous starting pitching.
4) The presence of Berkman, though not what he once was by any stretch, will deepen the Cards' Pujols/Holliday lineup, and release some pressure on the younger guys like Rasmus. Berkman could be the move that clicks the lineup right.
The arguments that Pujols is prone to injury and the corner OF defense is lousy are very valid. A prolonged injury to Pujols could sink them immediately. Berkman being just a joke in the OF, or an injury to Rasmus, who will be picking up the OF defense slack, could sink them too. But I don't expect them to be anywhere near as bad as they were last year...