Doc Searls writes about people he'd like to see have blogs who don't. His list: I'd add Don Norman, Jakob Nielsen, Kalle Lasn, Watts Wacker, George Lakoff, James Gleick, Steven Levy, Alvin Toffler, George Gilder, David Isenberg, Dave Farber, Geoffrey Moore, Esther Dyson, Mary Modahl, Hal Crowther, Rick Levine, John Naisbitt, Randall Stross, George Lakoff, Mike Wallace and Peter Drucker, to name a few.
There's a good reason virtually all of them don't (except Rick Levine and possibly a few others whose names I don't recognize): they're paid so damn much for the pearls of wisdom or idiocy -- depending on your opinion of them -- that fall from their lips that there's no currency in simply being read for free online. Most of these people have an immediate blogspherical distortion when they say anything meaningful in any medium: you can practically see the blogworld ripple outward from the shockwave generated by their utterances.
How many times do you see Farber, Dyson, Toffler, etc., etc., say something that's spread to hundreds or thousands of blogs and print/online articles? The same effect that drives people to a few blogs more heavily than many others -- see Clay Shirky's essay that Doc references -- works in terms of the non-bloggers, too. The people who have influence who don't blog maintain that influence in part because of their sway over traditional media which disseminates their bon mots to the blogging world quite effectively.
(And an interesting second-order effect: Clay links to books in his essay via my isbn.nu book price comparison site. Because of the great interest in his essay, which has been linked from practically everywhere, I am seeing several hundred clickthroughs a day to isbn.nu, some of which obviously result in book sales on which I get commission. So the irony is that Clay wrote something for free and published it and I'm reaping the cash benefit. I'll be sending him a thank you.)