No. For The Pitt, Mothership Zeta, and Point Lookout, your character is given a notice that there is something going on, and it ends in your character being transported to a whole new map separate from DC. Completely unrelated to the storyline.
For Operation: Anchorage, your character takes part in a simulation of the war that led to the nuke. Again, completely unrelated to the storyline.
For Broken Steel, the main storyline is essentially extended. This is the only exception, as to continue the main storyline, you have to first beat the initial storyline. However, the level cap raise is in effect regardless of progress in the storyline.
answered Jun 15 '10 at 15:21