Today, the average GPA at private universities is 3.3, a B+, while that at public colleges is 3.0, a B. From a study of 230 American Universities.
Link:
http://www.theatlantic.com/education/archive/2015/01/same-performance-better-grades/384447/
Left off from the original post: the data referenced in the article appears no more recent than 2007. Not sure how much value this article is today.