Like David Edelstein, I have neither expertise nor desire to speculate on the cause of David Carradine's death, but I wanted, belatedly, to second his description of the late star's unique brand of cool:
His vaguely Asian physiognomy made him suited to kung-fu and Zen masters, and his acting had that same alert detachment. You rarely got the sense that his roles cost him emotionally: Unlike his brother, Keith, who has been known to take risks, David had an inviolable sphere of privacy. But he never condescended to his material, even when it was risible, and his amusement was contagious.... David Carradine didn’t seem given to advance planning, career calculation, control. He was the anti–Tom Cruise.
Colleague Henry Riggs points out that David Carradine was #5 on the exhaustive "Center of the Hollywood Universe" list at The Oracle of Bacon. That is to say that, according to the site's algorithm, he is the fifth-easiest actor to connect to other performers in "Six Degrees of Kevin Bacon" fashion. Number one, appropriately enough, is Dennis Hopper; Bacon himself, ironically, clocks in all the way down at #507, between Harry Carey Jr. and Saul Rubinek.
As Henry notes, the list essentially measures longevity and an inclination never to turn down work--both family traditions for the Carradines, with father John joining the list at #143 and brother Keith at #199. David Carradine may not have appeared in many great films, but he appeared in a great many and, in my experience, they never suffered from his presence. Rest in peace.