http://news.netcraft.com/archives/2003/11/03/november_2003_web_server_survey.html
There are probably better stats out there, but as at 2003, this survey shows apache/linux with 67.41% of the web server market with microsoft sitting at 21.02%
Obviously those stats are out of date, but it does highlight the fact that linux based web servers are more popular than windows.
i'm amazed at what you can get for your dollar with linux. my laptop runs Suse and it's just as capable as my windows work station but the software is about 1/100th of the price. it's also a pleasure to code in open source.