In the BtB Power Rankings, we apply a 22.5 run/season bonus to the offense and defense of AL teams, and a similar penalty to NL teams. This is a very large adjustment, and makes it very hard for most NL teams to qualify in the ranking as a 0.500+ team (which makes the Dodgers' first place spot all the more impressive).
Why do we do this? Look:
Vertical bars indicate the American League winning percentages. The line is a 2-year moving average to help smooth out the fluctuations.
Starting in 2005, the American League began to dominate interleague play--one of a number of reasons that we think the junior circuit has superior talent, and a superior level of play, compared to the National league. It seems to have more or less stabilized over the past three years, but I'll update this graph after this year's interplay is complete. It's not unreasonable to think that a 0.500 team in the AL would be a ~0.570 team if they instead played in the NL--that's 92 wins, and a likely playoff berth.