Well if you see Some MVC Frameworks you see some code in a special file .htaccess
like that.
RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php [QSA,L]
This rules define the Url rewriting mechanism. So your example url is treated as :
Actual Url : http://www.hilariousworld.com/On2wheelz/index.php
Query String : /admin/adddeals/adminhtml_adddeals
As .htaccess already redirected all request to index.php with its query string parts. Now frameworks handle the Query String Part to determine what actual controller/action combination (in case of non-mvc applications requested content action ) need to serve.