His books are also very short. As in really short. As in "Don't you think this should be an article?" short.
That last phrase -- and I'll blog about it more in the future -- is a line I hear over and over again from people who think articles are short and books are long, and if a topic is focused narrowly then it's an article, not a book. I say it's up to the author and the market, but it is just fine to publish short books.
Authors come to me often with the stress that they haven't written "enough" for a book (whatever enough is). Sometimes they'll ask if their chapters are long enough in manuscript. Long enough? Hmmm... like you should add breadcrumbs to the ground veal to pad a chapter out if it's too short? How would I -- or you the author -- know when it was "long enough"? Would we hit a magic page or word count?
Personally I think length is irrelevant when considering either chapters or books, and I also have an enormous fondness for short. Not too short, not Hemingway short (I have no taste for his astringent style or for the recommendations of that annoying and terse Strunk & White book either) not "I didn't say what I meant" short, but tastefully brief, just-right, well-considered and well-said.