I've taken more heat than Daric Barton takes first pitch fastballs over my claim that, essentially, BA = OBP in the postseason to a first approximation. I've gotten it from just about everyone, with a few brave followers as well.
I picked up Baseball Prospectus' Baseball Between the Numbers: Why Everything You Know About the Game is Wrong and then found this lovely excerpt on Page 2 of ESPN.com
It's taken out of the chapter "Why Billy Beane's Shit Doesn't Work in the Playoffs" which was, I as I understand it, playing off of a quote from Beane. The book was published in '06, and was referring to why the earlier A's teams couldn't beat their opponents. Interestingly, at the time it was written, it was referring to the A's "meh" pitching in a few areas and poor defense. In 2012, it now refers to how the Tigers shut us down:
Of all the statistics in our our study, the one with the highest correlation to postseason success is opponents' batting average. Certainly, preventing hits is very important in the playoffs -- when you're matched up against good offensive clubs, it's vital to stop them from stringing together hits and starting rallies. But we also need to think about how a team can go about preventing hits. The best ways to prevent hits are: (1) to strike the batter out, so that he doesn't put the ball into play in the first place and (2) to catch the ball when it is put into play.
As I've said a bunch of times, low K's and high batting average guys, following the theory of BA = OBP in the postseason,is what this team needs to address moving forward or we can expect the same regular season success and postseason failure.