When atu2.com, which has very reliable sources, first wrote about this delay, they stated that the tour dates could be announced as early as January 24th, thus a 2 week delay from what was originally intended. At the time, their source was indicating a new tour start date of March 28 and that the location was moved from Miami to Los Angeles. If this is in fact correct, my guess is that U2's booking agents and Principle Management are working non stop trying to reroute the tour to accomodate Edge and are planning a couple backup plans, in case it needs to be pushed back further than March 28th or if down the road they decide the first leg needs to be cancelled. My own personal belief is that the fact that the tour start and thus at least the earliest first leg dates are in the Western US is primarily because of the fact that Edge has his home in Malibu. I feel they are looking for a way that allows the tour to go forward in the US, while allowing Edge the opportunity to spend almost every night and all off days at his own US home. When U2 tour, they generally have several hub cities around the world where they stay including Los Angeles, then they will fly on their chartered plane to the nearby cities on the afternoon of a show, and fly back to the hub city immediately after the concert ends.
If that March 28th start date was actually pretty firm, they really could hold off delaying the tour announcement until late February to early March, as their shows will sell out very quickly anyway, without much advance notice needed. If the March 1st Miami start was still going to happen, they really would have til early February to announce the tour.