In CEH Footprinting Part 2, Mike and Sean are puzzling how the OS can be Linux but the Web Server Microsoft IIS. The conclusion was "some kind of load balancing", which is correct. But there is more: the site uses CDN (Content Delivery Network) technology, where a CDN provider sucks data from a "master" web server and duplicates it on its own servers throughout the world for clients to use. It may not be on the CEH exam, but is technology worth knowing about.
I think the most important take-home point is this (mentioned in the Getting Started segment, but worth emphasizing): DNS names owned by a company can and do point to other company's servers. Cloud technology is one example. CDN is another. Yet another is outsourced sites (often used for job and merchandise sites). So if a report from Netcraft (or some other source) shows a company as the "Netblock owner" that isn't the one you have an agreement with, don't do any penetration testing on their servers!