Regarding w3techs statistics, 84% of web servers are based on Apache and Nginx open source software. Therefore methodologies they use do not count subdomains.  It means that all traffic to subdomains (126M unique visitors per month) they count as one. The same thing with and free subdomains.

There were studies with including revenue in market share comparison. Keeping in mind the fact that Linux cost nothing these studies could not hold any criticism and today are deleted from servers, but old posts like Quora 2013 still can be found where people talking  47.9% of the servers worldwide ran Windows Server whereas 40.5% ran Linux.

Closest to the truth looks W3Cook’s in May 2015 made an estimation of 98.3% Unix-like and 1.7% Microsoft Windows WWW servers.

This very site you are reading runs on Linux Apache web server.