I'm more concerned about the loss of quality. The fact that the audience wants simple games doesn't mean they want rubbish games - even Nintendo falls into the "shovelware trap".
Super Mario Bros. was a simple game, yes, but it had fantastic level design, catchy music, a well thought out "mythos"* and most importantly a sense of progression and development - the game got harder through the levels until you felt you'd achieved something by beating it.
All of this "casuals don't want goals, they want 'free roaming'/'everyone's a winner' mechanics" like Animal Crossing or Wii Music is rubbish too. Games need to be accessible but rewarding.
Let me give you some examples of this - these games are accessible and rewarding, and sold well amongst core fans and casual players:
Pokémon Red/Blue
New Super Mario Bros.
Super Smash Bros. Brawl
Mario Kart Wii
*That doesn't mean story or dialogue. It means the characters fit with the levels fit with the enemies, so that the result was "predictable" within the framework of the game, i.e. it was easy to see that lava was dangerous and coins were valuable. Nothing was out of place.
