The federal government recently adopted ICC (and NEC) as the official federal building code for DoD, NASA and a few other agencies, wheras they always had their own special codes before. Many of the code changes in 2008 seem to have been driven by experts in government agencies that never really cared before, but often have unique requirements that weren't adequately addressed, or lessons learned that apply just as well to the commercial world. Article 708, for example.
That, and the internet is making it easier and easier to collaborate- we all saw and discussed the proposed changes to 2008. How many of us saw the same for 2005? I bet it's WAY more than reviewed 2002 or 1999 or 1975. More collaboration = more feedback = more changes.
