It DOES support Apache if you want it to, and if you explain things the right way. The plug-in API just happens to be mod_proxy instead of anything else.
The customer gets Apache and can configure it as he pleases.
For example, the installation I manage uses some fancy mod_rewrite stuff to closely mimic previous URL structures that lots of external links take for granted. We map three different application servers into the general URL hierarchy (in addition to AOLserver), and let Apache handle SSL under a common certificate (just needed to convince ECommerce NOT to require SSL). This is also scalable to a multi-server setup BTW.
For all intents and purposes, we're running Apache!
As for IIS ... well, I still don't understand why some folks voluntarily jump out of a perfectly working airplane, either.
--Peter
PS. Why not make a clone of mod_proxy and call it mod_oacs?
(Just kidding 😉