Nginex It works fine - tested and everything with nginex, right - and nginex is suppossed to serve more pages with less memory and cpu usage thatn apache 2.4, right?
nginx is faster and uses less resources then apache, but it also has less functions, especially no .htaccess support. When you plan to switch to nginx, you should evaluate first if it provides all functions that you need for your sites as it is not a simple drop in replacement for apache.
The "nice" URL features of these cms systems will not work out of the box as the rewrite rules delivered as part of this cms systems will not work on nginx. You will have to trnslate them into nginx rules and insert the nginx rules in the nginx directives field of the website to get the url features working. So the cms systems will work on nginx, but you have to manually insert and adjust rewrite rules if you want to use all features of the cms systems.
Well Most people do not bother to optimaze apache webserver which can be rather slow with default settings. The point is that it can be slow and it can be fast. How apache performs is up to you.
You can find the correct nginx configuration for these CMS here: http://www.howtoforge.com/running-drupal-7.7-on-nginx-lemp-on-debian-squeeze-ubuntu-11.04 http://www.howtoforge.com/running-wordpress-on-nginx-lemp-on-debian-squeeze-ubuntu-11.04