Addressed in this article.

There's a growing anti-Bush meme, pioneered in part by Maureen Dowd and The New York Times, that holds that president Bush is a heartless chicken-hawk who wages war recklessly and cares not a whit for the welfare of the soldiers under his command. The evidence? That he hasn't attended any military funerals related to the Iraq war.
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The White House talks about preserving the privacy and dignity of the families of the war dead. But if this was really about the families, the president or Vice President Dick Cheney or Defense Secretary Donald Rumsfeld would be handing flags to widows and mothers in the time-honored way. - [from the New York Times]

This reference to the "time-honored way" does not, unfortunately, stand up under scrutiny. The History News Network provided a recent, helpful study of what the precise presidential tradition is in this regard.

They find no evidence that FDR attended military funerals, although, like Bush, he spoke of his empathy for those who had lost their lives and their families. Lyndon Johnson attended two funerals out of tens of thousands under his watch in Vietnam. Richard Nixon attended none. Jimmy Carter attended none--but he was present at a memorial service for those who were killed in his aborted mission to free the Iran hostages. The first president Bush attended no military funerals. Neither did president Clinton. Yes, they attended some memorial services--but so, of course, has the current president, most notably after 9/11. There is, then, no "time-honored way" in which presidents have gone to funerals for individual service members.

Like other such lies, expect the "only Bush doesn't attend funerals" one to float around for some months yet.