Although it's generally quite hard to get fired from Google, leakers have always been dealt with severely. Google once upon a time fired a member of the original Macintosh team for leaking information about the Christmas bonus.

My guess is that the increased closing off of various documents is to do with the increased amount of confidential partner-related information as Google scales its cloud business.

But, as is often the case with Google, much of the disillusionment here seems to be due to unrealistic expectations and nostalgia. There have always been secretive projects at Google. Chrome was super-secret; you needed special authorization to get into the Google+ area; you needed special authorization to get into areas where new Android hardware was being worked with; you needed special authorization to get into the X area; etc.