1- Nintendo built the Wii specifically with low power consumption in mind (they said so in one of their roundtables with Iwata). That goes a long way towards making the console reliable.
2- The Wii is an updated Gamecube, so it's likely that Nintendo has used a lot of the chips the Gamecube had. These chips are proven to be reliable after years of Gamecube manufacturing.
My Mario Kart Wii friend code: 2707-1866-0957