Basically, the guy is a genius. Read his Wikipedia bio.

Praise of the man:

"The one talent of David's that stands out is his ability to lay out a course of action that would take into account any sort of complicated facts and develop a far-reaching scenario. It's a chess player's sense: If I do this, the following 15 things are going to happen, and if step 11 goes so, I'll do this rather than that. It's a fantastic game-playing ability." Thomas D. Barr, quoted in the New York Times Sunday Magazine, June 1, 1986

"The Boies memory is one of the first things cited when people discuss his strengths. What's most impressive about that gift -- focused as it may be by the intensified concentration that his dyslexia demands -- is Boies' uncanny ability to recall a key fact, legal citation or piece of contradictory testimony at moments of the most intense pressure." Time Magazine, "Get me Boies!" by Daniel Okrent, December 25, 2000

A trial is a problem in maximizing the reasoning, under law and supported by fact, presented to a judge and / or jury. Those audiences have limited bandwidth to begin with. The "under law" constraint largely drives which reasonings and facts will be most important -- especially as all that must cross a barrier of evidentiary rules and trial procedure. The ability to weave all of that into a coherent narrative is crucial to communicating to the audience.

Boies can grab enough of the subject matter to speak to the key legal issues, and to ask experts the questions that define the boundaries around those questions. Another lawyer might know more of the subject matter, but that won't matter if they can't translate that extra knowledge into legal strategy.

Remember also that while you might be able to find legally pertinent technical responses to Boies' work in court, you're reacting to that after hearing his strategy. Good trial communication requires telling a unified narrative -- if your story doesn't already provide a basis for your response, that response will be weaker and may even distract from the story you do have. Boies' ability to anticipate arguments, mentioned by another comment, is crucial to all this -- it's not enough to have an answer, you really need to have that answer in advance of his question.

It's his "trial" skills. There is a team of lawyers, each lawyer skilled in one particular aspect of the case. Mr. Boies's specialty is pulling all the information collected/discovered by the various attorneys and creating a grand advoacy plan that includes strategy and argument. So an attorney incredibly astute at patent law may not be so good when it comes to verbal argument (specifically, appealing to the sentiments of the jury is an art in itself, and few attorneys are able to master this skill) and overall case strategy, but is able to effectively assist Mr. Boies in preparing for trial.

As a former litigator turned startup founder, I can attest to the difficulty of assembling the right team with the ideal point man for a trial, and when you do find one you respect, he is worth every penny. David Boies is one such man - nobody has gotten fired for hiring him as the lead trial attorney.

Maybe for his litigation skills? I'm sure there's a large legal team behind the scenes that includes IP experts, but "litigation" is its own field - most lawyers never see the inside of a courtroom. There's rhetoric, witness examination, making motions and objections, and so much more than expertise in an area of law.

(IANAL but I helped AOL sue Sanford Wallace, and it was a sight to behold.)

He seems to lose a lot too.

You bring out the best person for the toughest jobs, not the easy ones.