They have, but note the corollary to 'perfect emulation takes huge amounts of computing power': imperfect emulation can often be done cheaply.

The question for WBE is whether brains are the very rare SNES game which must be perfectly emulated to work at all... or one of the others. The success of machine learning stuff like deep belief networks, while using a fraction of the brain's computing power and minimal biological plausibility, suggests human brains aren't very special snowflakes.