Positioned correctly, could games like these -- and simpler ones yet -- be the gateway drug to draw players into World of Warcraft or other non-casual games? Runescape is a massive hit on Miniclip, after all. NCSoft packaged the character creator tool for City of Heroes as a separate app for the game's Korean release, before legal issues led to their pulling it down.
Here are a few "gateway games":
Any other such games you particularly like? Casual games that could be considered feeders into deeper game experiences?