No, Till, you're mistaken a little bit.
Nginx is not a web-server, it just proxies web-traffic. This is like a frontend in front of apache just to give out static files itself e.g. .jpg, .js or .html. But all the CGI-scripts it transfers to apache anyway (or whoever like php-fgm or Tomcat).
For example how it been performed by ISPmanager panel (BTW - your compete):
It puts nginx to port 80, and moves apache to 8080.
Traffic comes to IP.ADD.RE.SS:80 where nginx does everything it could itself and requests Apache on localhost:8080 to run CGI. Then Apache gives to nginx (localhost:80) all it compiled while CGI ran and nginx returns complete data to visitor.
This case is very helpful to offload Apache of dirty dumb work. It performs the only serious staffs like CGI cause Apache is heavy like an iron bridge
but nginx takes less memory space while doing the easy job.
Please take trial (2 week) license from ISPmanager and just check how it works overthere.
But the problem to realize that function will be when developer will synchronize nginx.conf and httpd.conf(apache2.conf). Both of them have to posses similar virtualhosts list.
We realy need nginx support for overloaded servers.
Actually this is particulary related to bug report FS#1017