Woodward's book is "Recommeded Reading" on the BushCo. campaign site, it was reviewed before release by someone in the administration, and various news organizations have vetted at least some of Woodward's sources. The Shrub himself is one of the sources. Colin Powell says they were instructed by the White House to speak to Woodward.
So when Powell and others in the administration start disagreeing with what Woodward wrote, what are we to believe? That the administration would approve the release of the book and it was full of mistatements by the very people likely reviewing it? That Powell and others lied to Woodward? That Woodward is telling the truth and BushCo. were too stupid to notice?
Which is it?
UPDATE: Or, as alert reader Wanda notes, perhaps it's ALL OF THE ABOVE.