apt - Why can't I purge apache2.2-bin and apache2.2-common?

I have tried to completely remove apache2.2 from my system. But the only thing that happens is that apt-get will remove "apache2-mpm-prefork" and install "apache2-mpm-worker".

I have killed all apache processes and tried in both Synaptic. and apt-get from terminal. Why won't my system delete apache, and why will it install "apache2-mpm-worker"?

Short answer: you need to purge the apache2 package as well as apache2.2-bin and apache2.2-common.

Explanation: this package is a "virtual package" - if you have it installed the system will make sure that one of apache2-mpm-event, apache2-mpm-itk or apache2-mpm-prefork or apache2-mpm-worker is installed. Note that these four packages themselves each depend apache2.2-bin and apache2.2-common.