Of course, Joe the Plumber and company probably don't realize that, over the last few thousands of years, the Bible has gone through countless revisions, additions, omissions, translations, translations of translations, etc. And many of these, of course, are based on either innocent human error at best or ideological manipulation at worst.
When genuine science books come up with revisions, on the other hand, the reason is that new evidence has been shown to challenge some of our former ideas, and there is no sense in holding on to ideas that have been empirically shown to be deficient or at least inconsistent with other things we have evidence to believe are true.
Today we have a simple example of this idea: why Pluto got "demoted" from the status of planet to the master of the Kuiper Belt:
And if you want a more detailed explanation of our changing views of Pluto (and the reasons why), NASA has a nice video. And if Neil deGrasse Tyson is more your style, you can check him out talking about the whole Pluto debacle, including all the hate mail he's been getting from second graders, or you can check out his NOVA documentary The Pluto Files.