While roster depth can certainly be most important as teams battle for 162 regular games and often lose key players along the way, a lack of talent at any particular position can still be exposed in the postseason.
The Nationals' decision to shut down Stephen Strasburg late in the 2012 season factored into their NLDS loss to the Cardinals as Edwin Jackson and Jordan Zimmermann each had rough starts. After two wins to start their NLDS matchup against the Giants, Cincinnati ran out of gas and lost three straight to a much deeper squad.
The 2012 Orioles, one of the biggest surprises of the year, were able to take the Yankees to five games in the ALDS. But in the end, they just didn't have enough hitting—they combined for a .498 OPS in the series—to get to the next round. Same with the A's, who didn't have enough offensive firepower to get past the Tigers and their dominant starting rotation.
For these playoffs, the Dodgers will have to cope with the loss of star center fielder Matt Kemp, who is out for the year with an ankle injury, and with his backup, Andre Ethier, who is battling an ankle injury of his own and might only be available for pinch-hitting duty, if that, in the NLDS.
With Skip Schumaker the likely replacement, the Dodgers lineup isn't the same. When half of your lineup consists of Juan Uribe, A.J. Ellis, Mark Ellis and Schumaker, it's hard to think you're World Series-bound.
Here are some other key roster-depth issues that could come back to hurt four playoff teams.