Once upon a time, most of the best first basemen in baseball were in the National League. Albert Pujols dominated in St. Louis. Prince Fielder was in Milwaukee. A-Gonz was in San Diego and Ryan Howard had both Achilles tendons, and Joey Votto was a rising star in Cincy. Hell, you can even reach and point out Mark Texeira's stay in Atlanta as roughly cotemporaneous.
And now...bupkis. Votto's the only one left standing (see: Howard, Ryan). Behind him, at least until Howard makes a comeback, is who? Ike Davis? Freddie Freeman? For the love of God, Mike Morse? As what is considered the premier offensive position on the diamond, the place where you're willing to live with a Dick Stuart's Strangegloveliness because he whales the tar out of the damn ball, there's nothing left. It's Votto and a vast wasteland filled with skulking Loneys and LaHairs and fossilized Heltons.
What this means, on one level, is that the NL - after some progress - has once again slipped back away from the AL in terms of quality. You just don't make up a Pujols' worth of offense anywhere else on the diamond, not unless you have a vintage A-Rod type at shortstop. And as good as Troy Tulowitzki is, and as many Scrabble points as his last name is worth, he's not A-Rod. (For one thing, way fewer pictures of him as a centaur.)
Part of this comes from various AL teams being cash-rich at the right time. A new TV deal for the Angels got them Pujols; the Yankee and Red Sox regional sports networks are licenses to print money. And part of it is the fact that the AL does have the DH - a place to stash those aging sluggers as they get older and slower, and still derive some benefit. Think back on the chatter on the Ryan Howard contract; one of the most common memes was that they'd have to trade him to the AL at some point on the back end of the deal because he'd just be a DH. AL teams don't have to worry about making that deal. They can just slide the immobile slugger over at some point without skipping a beat, and that allows them to go longer on contract offers than NL teams. That in turn means more money, which means lots of big guys who hit the ball a ton going to the AL.
At some point, hopefully, that will change. As the Freemans and Brandon Belts and Anthony Rizzos and Yonder Alonsos of the world get some time to develop, as the ownership situations in Los Angeles and Chicago settle down and those teams start flexing their market muscle, as the current crop of guys ages, then maybe the NL will catch up again. In the meantime, though, the AL's got the advantage, and that will show in the All-Star Game, and thus in the World Series. There's a lot of reasons to dislike the fact that the leagues play under different rules; this is one of the more subtle - but possible one of the most important - ones.