Just a note to interject - even in that article it's confusing because they use the word duplicate as well as syndication.
duplicate content is the same content on the same URL - which GWM talks about further in the article
I believe that a post on google + and the same content on the company's website is instead syndicated content - think press releases - many companies post them on their website as well as putting them in syndication. And then its up to the SE's to decide which identical version(s) serves as the best of all that are in the index.
I do a fair number of website audits and find (unintended) duplicate content all the time on the same URL.
And I agree doing a unique summary on google+ to lead a visitor over to your page. That way you're not competing with your own content for google to rank your website page over a google+ post.
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