It is a combination of things: 1) The DH. AL teams have a huge advantage because, in theory, offense is anchored by a professional hitter who by the nature of the DH rule removes the worst hitter from the line-up. Because of this, AL teams have 2) Better pitching. Pitchers need to be better in the AL because of the DH. Of course, AL teams can afford better pitching because, overall, 3) AL teams can pay pitcher premium salaries due to overall (not always, but overall) club salaries. Also, because of overall salaries and the need to combat better pitching, AL teams tend to be able to pay more for better hitters. Over time, these factors have created a feed-back loop upon which AL teams must commit to in order to create improvement. NL teams have a different model and rely more on quality bench players which are needed for pinch hitting and substitutions in a game.

AL teams playing at NL parks are at a disadvantage is ludicrous. Am I really supposed to believe that an NL team is in that much better shape because its pitcher has been hitting all year and the AL pitcher hasn’t? That may be the most minimal advantage ever. On top of that, when a key pinch-hitting situation arises, the AL team has an EVERYDAY player on the bench ready to take an important at-bat. On the other hand, when an NL team visits an AL park, the NL team is fielding a lineup of 8 regulars and a bench guy. Meanwhile, the AL team has 9 regulars, and the extra guy is usually a highly skilled, highly paid, everyday DH. Now all of that doesn’t totally make up for the interleague disparity between the two, but it certainly does its part. But just remember, you never hear any of this from the talking heads on your TV…

This is a good NYT article on the phenomenon:

The cause is straightforward: A.L. teams have spent more money on players than their N.L. counterparts. In 2005, the average N.L. team had a $71 million payroll, while the average A.L. team’s was $75 million. Since then, N.L. spending has increased only slightly, to $74 million a team, while salaries in the A.L. have soared to $93 million a team.

Have more home games this year also?

the AL this year as of Monday?

i was hoping this year would see at least some progress in reversing AL superiority. i would guess money is the largest issue as well… i remember looking up the salaries a few years ago and found that the combined payrolls from either league was about even… with the NL of course containing two more teams. that’s a lot more money, and it’s not like it’s just the yankees as an outlier messing with the averages.
another issue that i hate is that the inherent differences between the leagues favor the AL in interleague play, which depresses NL records overall because the interleague games count just as much as regular games. i feel like this must add to the perceived notion that the NL is worser (not a real word i know) than the AL than it really is, because at the end of the year, there don’t seem to be as many good records in the NL.
could we at least win an all-star game? just once?

at least I didn’t get razzed for asking a dumb question

I think the AL clearly has an advantage because of the DH, but that does not explain the current disparity given what I see as the NL’s superiority. Just look at the stats. I had a hard time picking all-stars for the AL because I couldn’t find clearly deserving hitters at many of the positions.

IIRC, interleague play was pretty even after the first round but has recently went south for the NL. I think this is just a random blip in the data (small sample). Think about this: just as this last round of interleague was beginning: the Cardinals lost Pujols and Wainright, the Cubs lost Zambrano, the Phillies started playing terrible, the Mets fired their manager, etc. At the same time, the Royals got hot, the Tigers started playing like everyone expected all year, and on and on…I don’t think anyone seriously believes the Royals are a better team than the Cardinals, yet they have won 4 straight games. It’s hard to say the AL is better when the Cubs cleaned up on the White Sox and the Cardinals took 2 of 3 from Boston – but it all suffers from small sample size, so you can’t really draw any conclusions from any of it. How would the outcome of the KC sweep have been changed if Pujols had played in those games, which I remember as all being very close games?