Why'd they change?Because a Judge told them to come up with the definition.

But that's won't change much for the detainees at the U.S. naval base in Cuba - Mr. Obama still asserts the military's authority to hold them. But his Justice Department says that authority comes from Congress and the international laws of war, not from the president's own wartime power as Bush had argued.

...

The Obama administration's position on use of the phrase "enemy combatants" came in response to a deadline by U.S. District Judge John Bates, who is overseeing lawsuits of detainees challenging their detention. Bates asked the administration to give its definition of whom the United States may hold as an "enemy combatant."

oh, and on that torture suit brought by four British citizens who say they were beaten, shackled and threatened by dogs. The question is whether military authorities should be liable to prosecution if they order torture.

"The upshot of the Justice Department's position is that there is no right of detainees not to be tortured and that officials who order torture should be protected," Lewis said.