This points to one area of Apple's use of GPL code. Apple doesn't want code licensed under GPL v3+ so they're sticking with the GPL v2 codebase (and custom-backporting bugfixes?). Apple uses Bash v3.2, GNU Bash is at v5.2.
GCC was replaced with LLVM in Xcode 4.2, and GDB was replaced with LLDB in Xcode 4.5 and GDB removed in Xcode 5.0. see https://en.wikipedia.org/wiki/Xcode