This is complete B.S.. Even Zoo TV had shows that didn't sell out. Playing softer markets on weeknights = slow sellouts. I wouldn't worry about it at all, the stadiums in Tampa, Pittsburgh and Houston will be at least 90% sold out by show day if not completely sold out. I attended the 360 show in Pittsburgh, and it wasn't sold out. There was a speckling of empty seats throughout the upper reaches of the stadium. But even still, there were 55,000+ at the show, and the show still grossed $5 million+. I doubt anybody was too worried about a couple thousand empty seats, nor will they be this time.
Coldplay are probably the biggest CURRENT band touring right now. Check out some of their seating maps on ticketmaster, there are A LOT of empty seats in most of the stadiums they are playing, some of them are venues that U2 sold out in one day. The Guns n Roses tour has been all stadiums, and also have had a lot of shows not sell out. I've seen pictures and heard stories of the entire upper decks of the stadiums being curtained off, with those ticket holders being moved downstairs. That was supposed to be a big deal, Axl and Slash onstage together again... but not even that can compete with U2 playing the Joshua Tree.
I do think that the SOI debacle really hurt U2's public image, and I really do think that the slow(ish) sales of some of the I&E shows had to do with how turned off the general public was at the time. This really does seem like a good move to get some of the casual fans back on their side.