There are three separate applications. PMP & Plex HTPC are oriented toward HTPC users. Plex for Mac/Win, is oriented towards Mac/Win desktop/laptop users.
Plex HTPC (announcement), still under development, is the replacement for Plex Media Player (docs).
Plex for Mac/Windows (docs) is a separate application. It resembles Plex Web, and is not oriented towards HTPC users.
