This has been discussed a tiny bit 4 years ago, probably before "Releases" were a feature on the site: http://www.giantbomb.com/forums/delete-combine-requests-34/delete-hydrophobia-prophecy-492886/
Hydrophobia (Pure) & Hydrophobia Prophecy is 70% the exact same game, and should for all intent and purposes be one game page on the wiki. The PS3/PC release added some levels, had improved graphics and minor content changes. The story and the game is the same, and Prophecy is basically comparable to an HD remake/release (which do not get their own pages).
My guess is that we didn't have the "Releases" feature four years ago (I can't remember) and we didn't have a good way to add stuff like this which spawned a lot of extra game pages, but I definitely think the two pages should be combined, and have the differences described in the wiki and have the distinction between the releases in the releases tab.
If the pages are not combined, the Hydrophobia releases tab needs to be cleaned up as it's full of Prophecy releases that in that case should be moved/deleted. (I did not add them, I only cleaned them up recently.)