The Afghan war is growing increasingly unpopular, it was only a few months ago that most people supported it, now 73% think we should leave. Gordon Brown has belatedly attempted to reverse that today by making the case for staying, whilst simultaneously signposting a way out*.
Obama's dithering between the two options of escalating the war or winding down the NATO presence is putting other Nato leaders in an awkward position because they need to spell out a coherent position to their electorates. However without an American decision there is only one unilateral decision they can make. They can't promise to stay the course, because if the US decides to go the other way they would have to do a u-turn. On the other hand they can withdraw regardless of what Obama decides and if there is no American decision that is what they will have to do.
* As Dilbert creator Scott Adams points out, Gordon Brown was employing "the cat is on the roof" strategy of preparing the ground for an announcement.