Why are CIOs so slow to adopt Office 2.0 type ...

Most CIOs are cautious in implementing new technologies.

Clearly when you need to assure quality of service to the enterprise users you want to make sure the application is robust and scalable.

CIOs are also concerned from decentralization of content and of losing control over standardization of business processes across the enterprise. 

I believe other concerns that need to be addressed by Office 2.0 companies to encourage high adoption are:

1. Security and privacy
2. Openness and ease of integration
3. Easy to export data - when your data is hosted outside your company walls you want to make sure you can always get it back when you want to.

There is no doubt in my mind that office 2.0 creates a tremendous value of unleashing intellectual property and knowledge exchange within the company, helping connect people within the company and increases sharing and collaboration and. facilitating the conversion of  tacit knowledge to accessible and searchable content.

Because they think they know best, because they got to this point by doing what "we've always done and it worked" and because for a lot of them change isn't something to jump into lightly.  Some of this reasoning is probably sound, running with new technology may have issues with stability, reliability and when you're dealing with mission-critial applications and people who have been trained for years to do something a certain way - it's not easy to change them overnight.  However, I believe, with time they'll change their mind or... will simply be left behind.