To -lobjc or not to -lobjc?

GCC manual says:

file.m
    Objective-C source code. Note that you must link with thelibobjc
    library yo make an Objective-C program work.

And:

-lobjc
    You need this special case of the-loption in order to link an
    Objective-C or Objective-C++ program.

However, I can succesfully compile a program with simply:

$ cc prg.m -framework Foundation

Is it a linker default, when you include a framework? If so, where is it documented? The program gets linked anyway:

$ otool -L a.out
a.out:
        /System/Library/Frameworks/Foundation.framework/.../Foundation (...)
        /usr/lib/libSystem.B.dylib (...)
    --> /usr/lib/libobjc.A.dylib (...)
        /System/Library/Frameworks/CoreFoundation.f...k/.../CoreFoundation (...)