Justice Department officials who investigated the missing documents initially were persuaded that Berger must, as he claimed, have taken documents by mistake and then destroyed them to avoid having sensitive material in his possession. The plea agreement was based on the assumption that Berger was mishandling classified material - not manhandling it.
Now, however, it is clear that there was nothing innocent or inadvertent in Berger's conduct. He has something to hide and, whatever it is, he was terrified that at least some part of it would come out of a non-criminal hearing before the Bar. With no possible criminal charges to face, he could not have claimed a right against self-incrimination. He could no longer get away with saying that he took documents accidentally, took them only to prepare for up-coming hearings (why, then, take five copies of one memo?), or didn't intend to destroy them. He would, in other words, have had to say more than he has so far.
I have no good way to tell if this Berger affair is actually important, but I have no difficulty at all assessing its relative importance when compared to the firing of the U.S. attorneys.
Just imagine if Karl Rove was caught destroying every copy of some documents in an archive...