Ok, need to explain a bit more, haha.
MIDI is not really the right word, it's called "virtual orchestration", meaning that for most parts, no real instruments were used during the production of the music. This is also not completely true because by using samples, you are actually using short recordings of instruments, so if you trace the line back long enough you'll end up with a real instrument recording after all
When people refer to 'midi' they often refer to the General MIDI standard and the crappy internal sounds on those wavetable soundcards. This is very different. MIDI is a protocol and, as someone pointed out earlier, doesn't transmit any sound.
Hope that clears things up a bit