Reasonable or not, that is in fact what they are from a purely legal perspective. There is usually legalese involved with the licensing of the stdlib such that it explicitly disclaims derivative creation in this case.
This is not an uncommon thing to see. IIRC, the gcc compilers have an explicit exception clause that says that programs compiled with gcc (e.g., the output) are not affected by the GNU GPL. A compiler usually does more than just transforms code from a higher-level language to a lower-level language. It can reorganize the code (-O2, -O3, -O4); it can inject standard or custom implementations of common behaviours that the user didn't explicitly write.
From a very real and very strict standpoint, a compiler/code generator does create a derivative work (and there's at least one code generator I've used in the past few years that holds this to be true explicitly; gSOAP) that is a combination of your copyrighted code and the code by the compiler writer (and possibly others involved).