As an example: On my Solaris server at home I have installed the sun C-compiler. However, the pike binary package I installed was built using gcc.
It's not possible to build modules with pike -x module with 'complex' (or old) style modules.
To get it to work you really do need your own configure tests instead of relying on the results of the ones done by pike at compile time.
The 'simple' (or new style) modules gives you everything you need to do that, that is, the location of pike includefiles etc.
The autodoc generation actually does not work at all unless you have the sourcetree installed (same goes for the testsuite, unless I am mistaken). So that's not really related to new or old style modules, unfortunately.