To put it in perspective:
Site A =
http://192.165.67.229/ (valid working demo), when you goto 192.165.67.229, its actually routing though a couple machines before you reach your destination, if one of the responders (via ping for a domain) gets attacked, the route is shutdown, but 192.165.67.229 remains online.
Why? This is because we route it though multiple machines before it reaches its destination, so if SERVER C goes down, lets say SERVER B kicks in, so attackers would have to find 100's of ips and launch attacks at every single ip, which is almost impossible.