Apple’s Mac OS X, Adobe Illustrator, Facebook, Google’s Chrome browser, the Apache MapReduce clustered data-processing architecture, Microsoft Windows 7 and Internet Explorer, Firefox, and MySQL — to name just a handful — are written in part or in their entirety with C++.
The key phrases are "to name just a handful" and "written in part."
It's very simple because most of this handful of a particular type of software are written in C, not C++.