Several sites on the internet number below or around Alexa 1,000 catering to these players - ArmorGames.com, AddictingGames.com (MTV), Kongregate.com, MiniClip.com etc.
For as many users as Facebook has it's still only 1/4 of the internet.
But that's true that it's only 1/4 of the Internet.
One game of mine that did about 1.2 million plays on portals peaked at I think 400 users on the Facebook version, which was promoted within the portal version.
Recently King.com launched a big facebook app called Funflow, which they linked to from over 100 games in ditribution and several large, many-millions-of-plays new releases. They've probably had close to 100 million plays across their games this year, yet their fb app hasn't quite hit 1 million users.