Had you told even an optimistic fan of the St. Louis Cardinals before the season that their team would enjoy a 13-game lead over the Chicago Cubs going into a game in the last week of July, they might have thought that sounded like a bit much. Had you told him that this would be so despite third baseman Scott Rolen missing more than 40 games and hitting a weak .235 BA/.323 OBA/.383 SLG when in the lineup, and newly acquired ace Mark Mulder spending most of the year trying to get his ERA below 4.00, he would have been all the more disbelieving. Had you told him that this would be so despite Cubs first baseman Derrek Lee making a very serious run at the Triple Crown and third baseman Aramis Ramirez slugging over .600, you might have been simply scoffed at. The Cardinals looked like a very good team coming into the season; but then so did the Cubs.

Partly, this big gap is the result of some typically bad luck for the Cubs. Shortstop Nomar Garciaparra has proved somewhat injury-prone over the last few years, but there was no reason to expect him to miss the entire summer with a torn groin muscle. Ace Mark Prior missed a month after being hit in the elbow with a batted ball. Center fielder Corey Patterson looked like a breakout candidate before the season, needing only to add consistency to his game to become a perennial All-Star; instead, he’s in Triple-A, his miserable .232/.270/.379 batting line only hinting at his miserable approach at the plate.

The Cardinals, by contrast, have had some good luck. Even Chris Carpenter’s biggest supporters wouldn’t have figured him for a 2.26 ERA at this point in the season, while longtime scrub infielder Abraham Nunez, owner of a career .311 OBA, has gotten on base at a .407 rate while filling in for Rolen.

Last night’s game, which saw Nunez and John Mabry – in a rather unlikely turn of events – hit mammoth home runs off Prior in the first inning, was quite indicative of the sort of season the Redbirds have had.

Moreover, though, the difference between the two teams reflect their fundamental approaches. The Cardinals don’t give up anything, from roster spots to outs, while the Cubs cheerfully squander everything from outside pitches to lineup spots.

Of the 11 Cardinals with more than 140 at-bats, for instance, only one – Yadier Molina, a fine defensive catcher who has only had 255 at-bats – has an OPS below .700. By simply not giving a lot of at-bats to utter mediocrities, the Cardinals have a considerable advantage over the Cubs, who have two players with an OPS below .700 – Patterson and shortstop Neifi Perez, who have soaked up 675 at-bats between them. Patterson and Perez also happen to have spent huge amounts of time atop the order, ensuring a minimum number of runners on base for Lee, who is hitting like Lou Gehrig in his prime.

Giving key table-setting roles to hitters like these, whose count-working skills were miserable enough to leave them with on-base averages around 100 points lower than Lee’s batting average, is not only inexplicable, but consistent with the Cubs’ bias towards aggressive hitting, even when it doesn’t come with results.

The Cardinals, by contrast, are quite happy to give at-bats to the pesky likes of shortstop/leadoff man David Eckstein, whose respectable OBA of .360 is driven in large part by his ability to draw a walk.

You see similar differences in the way the teams build their bullpens. The Cardinals have four relievers with 25 innings or more and ERAs below 2.70, while the Cubs don’t have a single reliever with 25 innings and a sub-4.00 ERA. This is odd because the Cubs’ bullpen corps is by any measure much more talented. Todd Wellemeyer, Rich Hill, and Michael Wuertz are the raw material of a dynamic bullpen – they’re all young, with great stuff, decent command, durable arms, and whatever else you could want. The Cardinals, meanwhile, rely on the mediocre veteran likes of Ray King and Al Reyes, whom you wouldn’t even necessarily expect to pitch well enough to stay in the majors.

The main difference, so far as I can tell, is that Cardinals manager Tony LaRussa uses his charges regularly, in set roles against hitters who are susceptible to them. Cubs manager Dusty Baker, by contrast, is prone to take youngsters, bring them into crucial scenarios against hitters like Albert Pujols, watch them fail, and then not use them for two weeks. The difference between using King well and Hill poorly, or Eckstein rather than Perez in a similar role, isn’t all that much.

These are essentially marginal players in marginal roles. But when a similar edge is gained at position after position, teams with very similar cores of star players end up 13 games apart. A Cardinals fan might not have seen that before the season; a Cubs fan familiar with the foibles of Dusty probably would have.