The n64I prefer accuracy, but I didn't know I needed a super computer for it to emulate at 60fps.
* has a multipipelined CPU with FPU, at a reasonably "high" clockrate
* has a specialised video processing unit with very powerful blendmodes, etc. This can be programmable at will, just see Rare's releases.
* has a specialised signal processor for vector processing, as well as other tasks like compiling video drivercode and synthesising sound.
* has games that require precise timing between these components. If timing is wrong, things screw up (take for example Top Gear Rally, and MusyX audio system titles)
Not hard to see why it is magnitudes more complex than the SNES.