Look simple
Webserver is just that a separate computer usually that does nothing but allow people to view webpages and administrator to edit data.
Second to gain access to the Webserver you set a password to allow access by the administrator...
Now if you set the password to the web server to the same password as the Date base or other Applicational Servers he could inturn do harm to the hole network....
Generally you would set the Web Server to a different Administrator password then the rest of the network and also only allow those using the web server to edit content on the Web pages....
Know by default the Apache web server doesnt allow root or other users to access the Apache server with common names..
There is a config file that allows you to set permissions to the Apache Web Server...
This config file tells who can edit the webpages and web server....
Now I can't remember the config needed to allow access to the Web server to edit code...
Second you must understand how directory's work in order to change the target to point the webpages for instance you said webpages are to be stored in /var/www/html so if your going change the location of the webpages you must have administrative rights in order to change data........ or your going to get that this individual can't edit the pages or change the with out root or "/" permissions........
Meaning the user has no rights to make changes to the Web server or file system.....
Well good luck hope this helps....
Later....
Sorry it took so long to respond started writing a book on what a web server is.......
