BBC Expert's view: Blair looks bad in a lot of these pictures. The others are walking quite purposefully, but Blair is very stiff and erect, as if he has stopped - the others all look as if they are moving forward.
Weegee's view: Obviously Blair is NOT stationary, or else he would not be "next to" the other leaders. It is a selective editorial decision to run with a photo that has him out of step with the others. The 'expert' is using these words to draw an allusion to Blair politically.
Photograph someone walking down the sidewalk (consecutive images) and some will be better at conveying motion than others. Now work with multiple figures walking. You may like aspects of one image more than another. That is the secret. Sometimes it is best to "overshoot" coverage so that the editor has more photos to choose from.
This is a continuation of the type of jabs the press took at Bush running audio gaffes (when they heard the same speech delivered without flaw several times that week) or scowling images.
All I would "read" into that shot is that Tony Blair has a sore back, for whatever reason. He's moving almost as if he's wearing a brace.