The Cards are currently defying their statistics. It's tough to do that for an entire season. The D-Backs did it last year, as they got outscored and managed to win 90 games, but it doesn't happen often. The best column to pay attention to at this point in the season is the "XW-L" column in the standings on MLB.com. That column takes a team's performance statistically (runs scored vs. runs against) and plays it out to show what their record should be based on how well they are playing.
If it wasn't a 162 game season, that column wouldn't matter, but with that many games, it usually gives a better gauge of where teams will end up. As of today, these are the standings in the NL Central:
1. Cubs - 49-33
2. Cards - 47-36
3. Brewers - 44-37
This is what the "XW-L" column shows:
1. Cubs - 50-32
2. Cards - 44-39
3. Brewers - 40-41
The Cubs have outscored their opposition by nearly 100 runs. The Cards have outscored their opposition by 28 runs. Using these numbers, the Cardinals have a really good shot at the wild card, but most likely they'll have trouble keeping pace in the division race for the entire year.
And the reason I mention this column is that it was very prophetic last year. The Brewers' overall record midway through the season was significantly better than their XW-L. The Cubs' overall record midway through the season last year was significantly worse than their XW-L. However, the Brewers luck finally ran out, as they hit a skid and fell back closer to in line with their XW-L, and the Cubs luck finally turned, as they went on a run to win the division.