Now it's a rarity.
Boston and St. Louis are the first since 1999, when the New York Yankees swept Atlanta.
"You definitely have to be hot and play good baseball, maybe for a little bit longer," Boston pitcher Jake Peavy said before his Game 3 start Saturday night.
From 1903 through 1968, the top teams had to meet in the World Series. There were no playoffs.
Then the AL voted in May 1968 to split into divisions the following year when the Kansas City Royals and Seattle Pilots joined to create a 12-club league. While the NL was adding the Montreal Expos and San Diego Padres, it initially refused to start a playoff.
"It would be a contradiction of baseball history and tradition to divide the league and then see a team that finished fourth or fifth in percentage playing in the World Series," NL President Warren Giles said at the time.
Two months later, the NL gave in when owners met again in Houston after the All-Star game at the Astrodome. The two division winners would meet in a league championship series, initially best-of-five and then expanded to best-of-seven starting in 1985. In the 25 years of a four-team postseason, the World Series featured the top teams in each league just nine times.
Then in September 1993, a year after Bud Selig became acting commissioner, owners voted to split each league into three divisions the following year and add another round of playoffs, a best-of-five division series. The postseason would double to eight teams.
The vote was 27-1, with Texas Rangers owner George W. Bush the future president the lone dissenter.
"I made my arguments and went down in flames," Bush said. "History will prove me right."
After a one-year delay caused by the 7 1/2-month players' strike, the expanded playoffs began in 1995, when teams played a 144-game schedule because of the walkout. The top teams met that October, with Atlanta defeating Cleveland in six games.
It didn't happen again until 1999. And after that until this year, the second after the playoffs expanded to 10 teams with the addition of a second wild card in each league.
"That's another manifestation of how tough it is," Selig said this week.
Selig defends his system, pointing out fewer teams make the MLB playoffs than in the other major leagues (12 of 32 in the NFL, 16 of 30 in the NBA and NHL).
Some refer to the postseason as tournament baseball. Playing well at the right time is more important that excellence and consistency over the long haul.
The 2001 Seattle Mariners were the biggest casualty. They went 116-46 during the regular season for a .716 winning percentage, the best in the major leagues since the 1954 Indians went 116-46 (.721). Seattle lost the ALCS to the Yankees in five games.
"Doesn't matter if you won 85 to get in the playoffs or 185 to get in the playoffs. It's how you finish," said Aaron Sele, the loser in New York's clincher.
With the advent of the one-game, winner-take-all wild-card playoff, winning divisions has taken on more urgency. For more than a decade, the main difference between division winner and wild card was home-field advantage.
"That one-game playoff is a nightmare," Cardinals pitcher Adam Wainwright said.
But now that the postseason is a monthlong event, the hurdles to get a ring are many. Just reaching the World Series is a major accomplishment, maybe more so than it was from 1903-68.
"Getting here and what's it taken to get here with a great team and a great group of guys, you see just how hard it is to win the World Series," Peavy said. "You really understand the preparation, the will of not just a few guys, not just a handful of guys it has to be an organizational philosophy that you're going to win the World Series. It's got to be a team and a group of guys that just refuse to quit and all put their efforts together as a team to be on top."