The exception has been Ali Hamza al-Bahlul, who helped al-Qaida produce propaganda and handled media relations for bin Laden and refused to participate in his trial. He was convicted in November 2008 of multiple counts of conspiracy, solicitation to commit murder and providing material support for terrorism, and is serving a life sentence at Guantanamo.
But experts note that in general the men convicted so far seem to be faring better than detainees charged with terrorism in civilian courts.
"Military commissions have produced sentences or plea deals that are lighter than those typically coming out of federal courts, where terrorism-related sentences are often very severe," said Matthew Waxman, a professor at Columbia Law School and former senior Pentagon adviser on detention issues.
It's hard to generalize about the reasons for the lighter-than-expected sentences since the facts in each case are so different, though clearly at least three of the plea bargains could produce significant assistance prosecuting more major figures.
The chief prosecutor, Army Brig. Gen. Mark Martins, declined to spell out any kind of prosecution strategy or to say which cases he might pursue next. But he could be securing the convictions of relatively minor figures in order to build cases against prisoners such as Khalid Sheikh Mohammed, the self-proclaimed mastermind of the Sept. 11 attacks and more than two dozen other plots, and Hambali, the Indonesian terrorist leader.
In Khan's case, his lawyers said he was remorseful and wanted to cooperate.
"His decision to plead guilty and to cooperate was not an easy decision for him, particularly after everything that happened to him prior to his transfer to Guantanamo," said Wells Dixon, one of his civilian attorneys, who has said his client was tortured while in CIA custody before he was transferred to the U.S. base in Cuba.
The military tribunals have long been criticized as overly favoring the prosecution. They were first reformed by Congress and President George W. Bush in 2006, then again under President Barack Obama in 2009. Martins said they now prohibit prosecutors from using evidence gained through torture, but lawyers and human rights say the changes have not gone far enough.
Clive Stafford Smith, a lawyer for the British civil rights group Reprieve who has represented many Guantanamo prisoners, said the relatively short sentences have gone to men so desperate for freedom that they agreed to plea bargains and don't make up for harsh treatment suffered in the past.
"There are still so many negatives," he said, "that to rehabilitate Guantanamo Bay's reputation in world opinion would be harder than rehabilitating Osama Bin Laden's, to tell the sorry truth."