The FileMaker installer puts code into Apache's httpd.conf file to map the /fmi/iwp/ (and /fmi/xml/, etc.) paths over to Tomcat, which is a Java servlet engine that then connects to FileMaker's Web Publishing Engine.
for the code added to httpd.conf, and:
for more info on Apache (Jakarta) Tomcat.
Ah! I did look in httpd.conf for a reference to fmi/iwp, but I totally missed all the FM includes at the bottom. Thanks, that totally answers my question (and then some).