* C++ is a standardized, well known, popular language.
* C++ is nearly a superset of C90 used in GCC.
* The C subset of C++ is just as efficient as C.
* C++ supports cleaner code in several significant cases.
* C++ makes it easier to write and enforce cleaner interfaces.
* C++ never requires uglier code.
* C++ is not a panacea but it is an improvement.
It's interesting to me how defensive many of those justifications are. "It's just as efficient!" or "It's just a superset anyway!" Not until halfway through the list do we get any real description of expected benefits: C++ makes it easier to write and enforce interfaces, and C++ supports cleaner code in several significant cases. The last item is the most telling though: it's clear that these developers feel they've hit a point of crisis, and they are willing to take risks like this in order to lift themselves out of the problem.