PhrozenDragon - exactly. It would be a big (huge) project just to separate all the information into the respected database. But from my point of view, that's the easiest way. The only other way I can think of would be to modify every page and add a "tag" (ie. for Diablo 3, it could be "Diablo3SearchTag") and then filter the search by that tag.
Either way... it would be a ton of work.