A note from Bob Ladd:
I just picked up and put away a book I'd bought in a second-hand bookstore before going to Romania in 1978, called "The Balkans in our Time", by Robert Lee Wolff, a mid-century Harvard historian. I realized that he's yet another example of a generalization that must somehow tell us something about how language works: Anglo-elite American academic historians often use their full middle name. Samuel Eliot Morrison and Henry Steele Commager come readily to mind, but Robert Lee Wolff fits the pattern, as does another more recent writer, Walter Russell Mead. And Andrew Dickson White, the first president of Cornell, was a historian. It's hard to search for these on Google, but I'm pretty sure I've noticed others, and I can't think of people who use their middle name and *aren't* American academic historians, except for good ol' boys like Billy Bob Thornton and Jerry Lee Lewis.
Actually, as I wrote the above I wondered about the Anglo-elite Harvard connection, and I realize I may be underestimating that factor and overestimating the historian factor. A look at the Harvard presidents website throws up James Bryant Conant (who was a chemist, apparently), and a further search of the mental lexicon produces John Maynard Keynes, who was certainly Anglo-elite but not American. Similar websites from other Ivy League-ish places suggest other such names, mostly from about 1850-1950, though they aren't people I've heard of so it's hard to be sure if they were really know by all three names. (The Cornell president website seems to list middle names for everyone, including people who I know didn't regularly use them. Penn seems to do the same.)
Obviously I need a vacation.
I believe that Billy Bob Thornton and Jerry Lee Lewis are instances of a different pattern, namely compound first names, where friends would call them "Billy Bob" or "Jerry Lee". I doubt that Samuel Eliot Morison's intimates called him "Samuel Eliot".
Conforming to the original pattern, there are also writers like Percy Bysshe Shelley, Henry Wadsworth Longfellow, and Robert Louis Stevenson; and politicians like William Jennings Bryan. There are also women, like Elizabeth Barrett Browning, whose middle name may have been retained out of deference to their name before marriage — EBB was born Elizabeth Barrett Moulton-Barrett.
Of course, there are quite different multiple-name patterns in other cultures: French compound first names, Russian patronymics, Spanish apellido paterno and apellido materno, etc.
And there's the maybe-related pattern of using a first initial and a middle name: E. Digby Baltzell, J. Fred Muggs. Or two initials, like E.E. Cummings, J.R. Ewing, or A.A. Milne. Or the occasional explosion of names exemplified in Milne's immortal lines
Weatherby George Dupree
Care of his mother
Though he was only three.
Anyhow, other LL readers in need of a vacation may be able to help us understand why certain English-speaking subcultures use middle names more adhesively than others. I imagine that there's even a scholarly literature on this subject, though I don't have time to look for it.
[Update — We shouldn't neglect the recent famous case of name recycling: our 41st president, George Herbert Walker Bush, and our 43rd president, George Walker Bush. There are apparently older generations of George Bush, and at least one newer.]