It turns out Defense Secretary Chuck Hagel did, in fact, attend the Greene funeral, a fact I should have known.... If I had looked into it just a bit more, I would have seen, for example, a Stars & Stripes article that
specifically mentioned Hagel's presence....
Curious about what Davis had said, I looked for any sign that Nixon had attended the Dillard funeral. I went to the
Nixon Library website, which has posted the minute-by-minute White House logs of Nixon's activities. They're very detailed; if Nixon had gone to the general's funeral, it would have been listed. I looked through the month after Dillard's death and found no evidence Nixon had attended. Likewise, it turned out Bush did not attend the Maude funeral....
Just to summarize the facts in this convoluted affair: Hagel did attend the Greene funeral. Obama and Biden did not. Nixon did not attend the Dillard funeral, and Bush did not attend the Maude funeral. There is no "tradition" of presidential attendance at generals' funerals that Obama "bucked."