Obviously, the "lengthy and repeated war-zone tours" are a hardship, but not more of a hardship than what was endured during the world wars or the Civil War or what have you. What you're seeing with these shortfalls, however, is officers responding to the fact that unlike in those previous grand conflicts the political class in the United States clearly doesn't actually regard the war in Iraq as a key battlefield in an existential conflict for the ScaryIslamoBoogieFascists. There's no mobilization on the home front that remotely suggests that George W. Bush or Michael O'Hanlon or anyone else really sees this mission as worth giving up anything for. So officers are responding in the same way.This sounds temptingly correct. But is it? Or is this a problem with every war that lasts more than three or four years?
Unfortunately, it's hard to say since the number of U.S. wars that have lasted more than four years is vanishingly small. The Civil War and World War II (for the U.S., anyway) came in just under the four-year mark and people were getting pretty tired of both of them by the time they ended. The Korean War lasted three years. No other big war in the past century or so has even come close.
Except for Vietnam, of course. And guess what? We had the same retention problem with mid-level officers during that war.
So: Iraq and Vietnam were both long wars. They were also both unpopular wars that required little real sacrifice on the home front. It's hard to say which is really at fault for officer corps itchiness, but frankly, I'd probably put my money on "long." Greatest Generation hoohah to the contrary, I'll bet that if they'd had a choice, lots of mid-level officers would have been getting out of Dodge in 1944 and 1945 too. But they didn't have a choice, and then the war ended. So we don't really know.