yeah, there are developers using a specific engine just for the Wii like High Voltage so theres no excuse for developers/publishers to optimized the Wii's graphics capability.
end of core gaming days prediction:
E3 2006-The beginning of the end. Wii introduced
E3 2008- Armageddon. Wii motion plus introduced. Wii Music. Reggie says Animal crossing was a core game. Massive disappointment. many Wii core gamers selling their Wii.
E3 2010- Tape runs out
http://www.fivedoves.com/letters/march2009/ICG_Tape_runs_out.jpg