Dungeon Finder is the “Looking for Dungeon” (LFD) system [Blizzard] introduced in [patch 3.3.0]
Patch 3.3.0 is a content patch that included [Icecrown Citadel] as a new raid instance as well as three 5-player dungeon wings in the [Frozen Halls] Patch 3.3 was to be the last major patch before the release of [World of Warcraft: Cataclysm]
Source: WoWwiki
It was not in original wrath, it was added by mistake at the end of expansion.
RDF was in original wrath added in 3.3.0, 6 weeks before ICC opened its doors. So RDF was available almost half of expac. Which makes it a Wrath feature, not a Cata as you try to imply here
See? You just proved it yourself that it was added in 3.3.0. and was avaliable only for a while at the end of expansion as a catch-up thing. Which dont makes it original wrath feature.