Somewhat unscientifically I took a look on Sourceforge and the top twenty projects/language break-down is currently thus:
- Java(43,199)
- C++(34,313)
- PHP(28,333)
- C(26,711)
- C#(12,298)
- Python(12,222)
- JavaScript(10,307)
- Perl(8,931)
- Unix Shell(3,618)
- Delphi/Kylix(3,353)
- Visual Basic(3,044)
- Visual Basic .NET(2,513)
- Assembly(2,283)
- JSP(1,891)
- Ruby(1,731)
- PL/SQL(1,669)
- Objective C(1,424)
- ASP.NET(1,344)
- Tcl(1,241)
- ActionScript(1,164)
Perl + Python together still total less than C alone. I have no idea why Java is so high, I know of no single Java developer and have not seen a single Java project, but I am sure someone is using it! For probably the same reason, you are not seeing much C/C++, you are just not working in a domain where it figures highly. I work in embedded systems where C and C++ are ubiquitous and Python comes nowhere. Different languages are encountered to different extents in different worlds.
You ask what you can do with C/C++ that you cannot do easily with Perl/Python; well the answer is plenty, real-time embedded systems for one; but if that is not what/need you want to do, then there is no reason to. On the other hand I might ask the reverse; I'd use C++ for things you might use Python for, simply because for me it would be easier and quicker (than learning a new language and getting the tools working)