Robert Spencer on the Osama "truce":

In Islamic theology traditionally the forces of jihad ask for a truce when they are weak and need to gather strength.

I'd have to say that this is a good bet because even if an American 7/7 is around the corner(and remember that the tube attacks came after Osama's last ultimatum to Europe), some two-bit backpack bombing isn't what Osama initially had in mind for an encore on September 12.