In the first place, the notion that Gibbon, Macaulay, and Carlisle addressed some mass public audience seems to me to be highly suspect. That they gave shape to history as a practice in the English-speaking world, I grant. But, honestly, how many people do you imagine have read Gibbon's six volumes of The Decline and Fall ... in the 225 or so years since they were published? Don't everybody raise your hands at once! As Healy points out, history sections in book stores are generally much larger than sections for political science or sociology, so some contemporary historians are meeting a substantial public demand.
In the second place, the notion of monographic building blocks to some larger structure seems to me no longer very useful as a way of explaining what we do. That metaphor fails because the thousands of blocks we produce are not cut to fit together. They shouldn't be because you'd have to know what you were going to find before you did your research in order to make it so.
Thirdly, so prolific have we become that we all have some difficulty"keeping up," even in our little sub-specialties. I can tell you where I know Taylor Branch's Pulitzer Prize winning book, Parting the Waters, is unreliable. It gives me grave doubts about its reliability elsewhere, but no generalist can be able to distinguish the gold from the dross in it. That some generalist has actually worked through and is capable of critical use of all the"building blocks" we have produced seems highly doubtful.
Finally, Tim's call for graduate education in history to include a portfolio of work addressed to a significant public audience strikes me as very sensible. And it ought not be shunted off into some program called"public history." The portfolio's rigorous scholarly article might point toward a monograph, but dissertations as"pre-monograph" are a dreary capstone experience. And, too often, they are riddled with the cramped, tortured prose from which Schama wants us liberated. Yes, I know, I've almost thrown out the baby with the bathwater, but don't let it hit you ... on its way out.
By the way, John Halbo and Belle Waring are guest blogging over at Crooked Timber this week and John has a terrific piece there, "Ecce Holbo", which posits a"golden age" of blogging. It's a terrific read. Poor man should have been a historian.