Corporations are usually control freaks about their image and the messages that they put out for PR purposes. So no wonder that they have not embraced the blogosphere. It is also hard for them to respond to outside people who do blog , and criticize them - because given the culture in the blogosphere, corporations are just not credible. There was some noise going on a while back about some employees being fired for contributing to a blog about their employer (check out Blogging at work and related article), and some people feel that companies are entitled to loyalty from their employees. Google fired an employee for blogging about his workplace environment. Basically, there seems to be a dearth of policies about this.
IBM is taking the lead in this matter, and has asked employees who blog to define guidelines. IBM considered the pros and cons of transparency, and decided to go for it. James Snell's posting Blogging at IBM gives the scoop and link to the guidelines.