I had expected that to be true as well, but when I tried installing a pure Perl module on a Mac OS X, I found that with the default installation the error

make: *** No rule to make target 
`/System/Library/Perl/5.8.6/darwin-thread-multi-2level/CORE/config.h',
+  needed by `Makefile'.  Stop.
[download]

arose. This was fixed by installing the Xcode package, which contains the C compiler.