The Wii U isn't expensive because of it's hardware performance.
It's expensive because Nintendo became obsessed with weird, niche-y hardware ideals like a system having to be as small as possible so it would be approved by Japanese moms. And having to have low electrical draw because uh ... well because of efficiency sake or something
That's why it requires a heavily customized chip. That and they thought throwing a 6 inch touch panel (and because it's Nintendo they have to use a resistive touch panel that no one else uses, everyone else is on capacitive).
All these weird, custom demands that Nintendo makes on their hardware means the hardware is not cheap to produce, it's heavily customized and Nintendo has to pay for that. Nintendo can't use an AMD GPU design from a perfectly good existing chip ... they have to have a completely custom chip designed from scratch to their needs, which again is expensive (honestly Yamauchi would not allow this). Much like the 3D screen on the 3DS is expensive.
Both MS and Nintendo have the same problem in that they also bet the farm on expensive controller gimmicks that have back fired in terms of sales appeal and are now weighing their respective console's down by keeping the price high.