Randy E. Barnett, in an April 17th Wall Street Journal editorial, Three Cheers for the Lawyers, figured it all out:

The point I decided to make was simple: For better or worse, we have an adversary legal system that relies for its proper operation on having competent lawyers on both sides. In every case I knew about where an innocent person had been convicted, there had been an incompetent defense lawyer at the pretrial and trial stages.

No, his point wasn't to castigate incompetent lawyers.  In fact, he goes on to praise the defense lawyers in the Duke rape case and use this opportunity to admonish the readers of the Journal that they too should bear in mind that lawyers serve a purpose other than as a pin cushion.

While he is undoubtedly correct that competent counsel is crucial to success in criminal defense (as opposed to the lawyers are fungible crowd who prefer to pretend that any lawyer will do when one's life is on the line), his statement above is either shockingly naive or disturbingly disingenuous.

So it's all about defense lawyer incompetence?  It has absolutely nothing to do with deceptive and deceitful law enforcement practices?  It has nothing to do with concealment of exculpatory evidence by the prosecution?  There is no impact of a court system largely inclined to pay lip service to the presumption of innocence while firmly assuming the opposite?  On what planet?

Never will I excuse inadequate representation by a defense lawyer.  But I will similarly not pretend that they alone bear the blame for wrongful convictions.  The prosecution side has weapons that the defense side will never have:  They have cops with guns and shields.  We are lucky to have clients who can afford a basic investigator.  They can pressure witnesses into saying, or not saying, what they want.  We get doors slammed in our face at every turn.  They can obtain information.  We are denied anything beyond the most cursory information.  It's not a fair fight, which is why the defense has to be a whole lot better than the prosecution if we are to have a fighting chance.

So thanks for the complement Randy.  And thank you, Mr. Wall Street Journal, for remembering that defense lawyers have a role to play in the system.  But let us not rest easy knowing that we have solved the problem of prosecuting, and convicting, the innocent by laying all blame at the feet of the incompetent defense lawyer.  The prosecution has a duty, a very meaningful duty, to make sure that the poor fellow they put through the wringer is not an innocent man (or guilty, but of a lesser crime than alleged).  Some prosecutors take this obligation very seriously; many do not.  Many more are too immature or blind to understand what this means, seeing their cops as perfect heros incapable of doing or being wrong.  There's plenty of blame to go around.