Manual:Wiki in site root directory

Why to, or not, use the root directory of a Web site as the wiki directory.

Template:Wiki-in-docroot links here and is used in Manual:Short URL. Details needed below.

Wiki specific domainnames or subdomainnames
I like these two hypothetical examples for sites that are predominantly wiki. If wiki is to be the dominant paradigm of a site, then no special wiki directory is needed and to use one is redundant and counter intuitive.
 * http://wiki.me.com/Article_name
 * http://wikime.com/Article_name

Why should above be deprecated? Please be specific, of course.