The prosecution made a mistake in over-estimating the intelligence of the jury. As someone above said, they should have "dumbed it down" a bit, and possibly used more 'flip charts' as Baez did, since the jury seemed to like those. *insert eyeroll*
Just to bring an opposing perspective to this - I just finished taking trial advocacy. The one thing my professor tried to hammer home to us is that any listener will start to lose focus after 6-7 minutes. Things like visual aids help refocus the listener and help reinforce your point. I think it's something like only 10% of a verbal presentation is absorbed. About the same percentage for visual - but when you combine the two, you get greater retention. It's not about intelligence at all, or "dumbing" things down. Flip charts and other visual aids can win a trial, simply because they help hold attention and hammer your point home. It's trial advocacy 101.
The prosecution was highly professional, intelligent, and didn't stoop to the level of insincere gestures (like Baez's fake smile and "good morning ladies and gentelmen.") It has been my experience that people of a lower intelligence level will interpret these traits as uppity, over-confident, stuck-up, arrogant, etc.
I'm sorry, but "good morning ladies and gentleman" is a well-used greeting by the prosecution and the defense in many, many cases. Authorities are split about 50/50 on whether it's good manners or comes across as insincere to jurors. It's something to consider - my professor said that greetings were always good when you needed to humanize your side of the case. Again, it's not about level of intelligence, it's trial strategy. To me, the prosecution came across a bit cold, and they might have wanted to humanize themselves a bit more. It may not have made a difference, because it is a 50/50 thing, but you really can't knock Baez for doing something that's accepted in practice and taught to us in schools as something to do.
Baez, on the other hand, kept things on these jurors' level, because he's not that bright, himself.... I mean, it took the guy forever to pass the bar! The jury related to someone of Baez's level, so they bought his story -- even though they were given a jury instruction that the lawyers were not on trial, and they were not to make their decisions based on how they felt about the lawyers. This is yet another way the jury disregarded their jury instructions.
It took Baez forever to pass the bar because the bar would not admit him for eight years because of failure to pay child support. It's not really an intelligence issue, necessarily. (I don't think it's smart to avoid paying child support for eight years, but that's another story). It wasn't about his ability or inability to pass the test. To be able to take the test to pass the bar, you must first pass a character and fitness test set up by the state's bar. That was what hindered Baez, not his intelligence level or lack thereof.
The lawyers are not on trial, no - but the manner in which they advocate their case does affect how the jurors view the evidence. Flipping the bird, laughing during closing, saying good morning, how close you stand to a witness, what you wear, how you address the judge, even the inflection or timber of your voice - this ALL affects trial advocacy. It's taught in schools, and there are thousands of books written about it. Neither the state nor the defense were doing anything wrong in the presentation style - they simply chose two different methods. In general, the state is more serious and the defense humanizes, but sometimes it can be more effective if those flip. Or if both hammer on the law, or humanizing. While I have issues with some things Baez did at this trial, I think you're unfairly knocking his advocacy style when it's an accepted and taught method of trial advocacy.