I'd really like to believe that prominent people _choose_ Linux and Apache, but often it is just because their virtual host provider uses it.
http://uptime.netcraft.com/up/graph/?mode_u=off&mode_w=on&site=www.edcase.com This seems to be the case, as it was for the Whitehouse (.GOV!!!) after that worm threatened to DDoS the site a year or two ago. The Whitehouse did not consciously CHOOSE Linux, they just went to a provider that just happened to use it as a load balancer or something.