I saw some talks on ASP.Net vNext this week and the links between .Net web apps and IIS are weaker than ever. I'm sure that .Net web apps will still be deployed to IIS when they need to scale a lot, and are hosted on windows, but neither of those two are mandatory any more. A lot of sites and web services won't need all that and can use a self-host or lightweight host. OR new hosts/adapters to other web servers can be written. There's a lot more hosting and platform flexibility coming, which is exciting.