Azumanga Daioh's simple and surreal characters readily lend themselves to AMVs.
Naruto's modular and replicable costumes readily lend themselves to cosplay.
Remember that Japanese is the majority language of the blogosphere. These guys understand user-created content. Is it mere coincidence that some modern anime lend themselves so readily to such specific forms of consumer evangelism, or are anime studios deliberately designing their content for fan mashability?