An Unorthodox Division lead

The D-backs are certainly playing some great baseball as of late, but a deeper look into their numbers reveals a disturbing statistic - this team has scored fewer runs than they've allowed. 502 scored, 523 allowed. Of all the teams in the division, they are most similar (based on these numbers) to the Giants. The Rockies, Dodgers and Padres all have positive differentials, in some cases substantial ones. Unless this is a trend from the beginning of the season, I don't see these baby-backs outlasting the Padres. Well, I guess that's why they play the games.