I know that this is a very old thread, but i have the same issue of understanding the "Memory Used" System Information in cpanel nowadays.
On centos 6 the above explains a lot to me, but now on centos 7 servers i am confused again:
Memory Used 56.55% (9,191,032 of 16,252,132)...
How can I get serverinformation to actually be off? I modified it in httpd.conf however using whois.sc/anydomain.com here you'll still see this with all cpanel hosts:
Apache/1.3.33 (Unix) mod_auth_passthrough/1.8 mod_log_bytes/1.2 mod_bwlimited/1.4 PHP/4.3.10 FrontPage/220.127.116.1135...