I may be wrong, but I'm not sure that anyone predicted that our pen would be a strength, but rather that it would not be a weakness, that it would be fine. I don't think it's necessarily been a strength, but I think it's been a lot better than you give it credit for.
Personally, I think the 'self fulfilling prophecy', which I like to refer to as confirmation bias, is working more the other way. Some people were so sure that our pen would be our weakness that every bad outing by the pen sticks out sorely, and despite the problems that we've had with our starting rotation and our offense, they are blaming the current state of the Sox on the pen.
Now, it's quite possible that from this point forward, our pen will be our weakness. The rotation and the offense, which were supposed to be great strengths, seem to be performing a little more consistently. But to date, the pen is still reason #3 behind the rotation and the offense for why the Sox are 6 1/2 games behind the Yankees.