Sure, three of the four other teams have losing records, but that's just because they keep losing to the Dodgers.
The division, as a whole, is playing .500 record. That means they are .500 against the other two divisions. (Duh.) To that the Dodgers only contributed a 1-2 record. The Giants won a series in NY and split a series in Philly, but are only 2-4 against the Dodgers.