Simply put, how are pages like these processed by the server or the wiki? Is there a directory named POW or do wikis use some kind of forwarding or masking to insert a literal slash in the URL?
From MediaWiki Subpages
In namespaces where the feature is switched off, any forward slashes (/) within a page name are simply part of the page name and do nothing special
Which mean, most of the times, they are just names. As digitxp said, Wikipedia works just like any other dynamic websites, consuming URLs and serve content from database queries. Technically, for large sites like Wikipedia most of the times the page you see is served from a Squid cache which store a static copy to be reused as long as it's current.
This behavior is only correct for Wikipedia. Other wikis could use different wiki engine with different caching strategy.