So, I was wrong
Thinking about it, it seems possible that, because they're so young, the Yankees' relievers may be going through a case of very ill-timed burnout.
Take Phil Hughes, for example.
By my count, Hughes has thrown 108 innings (counting playoffs) this season, his first as a reliever. The total is his highest since 2007, when he threw 110 1/3 between the majors and the minors. Additionally, it's the first season in which he's been regularly used on back-to-back days, which almost certainly added new stress to the 23-year-old's arm. More than likely, that has played a big factor in his postseason struggles.