If someone was sharing things that are private (our assumption), wouldn't it follow that they are sharing things that they have indicated (via some other means) are public?
For example, David Drummond's post on the Google Blog regarding Android patents (http://googleblog.blogspot.com/2011/08/when-patents-attack-a...). He has authored this post, indicated this is public but failed to share it publicly using G+. Is this not the purpose of G+?
These execs attend press events often where they openly voice their opinion in the public domain. It's a public company too and these people are actually accountable to the public.
However, it seems that although they share publicly when asked to by reporters and their open-ended questions they do not see G+ as a means to publicly share. They do not understand the value of information sharing and user generated content, the cornerstone of web 2.0. They are still stuck in a pull-based world driven by journalists asking questions. Facebook and Twitter understood the value of this change well by living through it (http://vaughan.io/post/10476571077/live-the-problem).
What we can draw from this is that its not going to be Google who jumps on the next big trend in social, if they can't even understand how to use their current product to its intended effect. They only built G+ because the concept was proven by Facebook and now they are just replicating it. Facebook will continue to lead the market here until the top executives like Larry, Sergey, Alan Eustace, etc. can understand their own product, its weaknesses and its strengths.