At the risk of second guessing the parent, they're considering the classical 'enterprisey' stuff as mainstream. If you look at what people use in most companies of a reasonable size, IIS is surprisingly common and Apache tends to only turn up when Java or PHP is involved, with appropriate nods to Oracle and IBM for their relative technologies.

Outside on the open Internet I absolutely agree that Apache and Nginx are the default HTTP servers. I switched from Apache to Nginx years ago (with a few exceptions) as it just seemed as though I could do more with less with it and it made sense for me to standardise.