this is true, Widi (wave to midi)is a program that can handle monophonic voices, with a little editing to get it right.
But it is just a question of harmonics. The harmonics of an entire orchestra playing together, all mixed together make recognising the fundamental frequencies very difficult.
With enough processor power it may be possible to work backwards to the fundamantels of each instrument. Maybe in a few years time this may be possible because the solution lies mathematically in crunching many numbers repeatedly until the pattern emerges.