I can spot, however, kernel-mode HTTP servers (including customized ones), and heavy use of pretty advanced stack with good optimization capabilities. The choices of the stack do make a big impact, something that they have mentioned several times, with the summary of "paying Microsoft licenses paid back very well compared to using popular open-source stacks"
Remember, Performance is also a feature. Both a non-functional one (to reduce your costs) or functional one (to have happier users).