I found out what was the problem so here is what was happening. (I'm not crazy, answering to myself and all, I just think that someone with the same problem may be interested in finding out what the answer to my question was! So there!)
I had Apache compiled by default when I installed the OS (linux) for the first time. I later compiled my own version of Apache resulting in duplicate apxs file and duplicate libexec directories. It's a bit more complicated than that but that's basically it.
When I was compiling PHP --with-apxs it was putting the new module in the first (obsolete) Apache's directory while httpd kept using the module I had originally created (without apxs -- when I compiled PHP for the first time -- I didn't know any better back then).
The moral of this story is: if you compile --with-apxs make sure you're using the right apxs, the one for the version of Apache that's actually running. You can do that by using --with-apxs=/path/to/apxs at compile time.
