The OSD's numbers above differ somewhat from the Department of Veterans Affairs. The VA has Vietnam-era veterans as 9,200,000, not 8,744,000. The number of those deployed to Southeast Asia is the same - 3,403,000. The VA doesn't have a separate number for those deployed to Vietnam.
The current estimate for the number of living Vietnam-era veterans is 8,122,000.
http://www1.va.gov/opa/fact/amwars.html
Terry, the item you quoted claims "Of the estimated 2.7 to 3.1 million Americans who served in Vietnam, approximately 1/3 (fewer than 1 million) are alive today...." As the numbers above note, about one million Vietnam-era veterans have died (9.2 million minus 8.1 million). Even if
every one of those was an in-theater veteran (which of course is not the case), the claim wouldn't be true.
Contrary to that claim, far more than "1/3" of Vietnam veterans are alive. 88% of Vietnam-era veterans are alive. Even if those who were in-country were dying at 2-3 times the rate as all veterans, more than two-thirds, not one-third, are still alive.