midi quality differs from computer to computer? I did not know that.
Yes, it depends primarily on the synthesizer capability in each computer's audio. Certain software synthesizers, like the Yamaha SXG, can emulate certain hardware. Results will vary depending on your sound card.
Midis are really just instruction sets and each computer plays them with what ever instruments it can simulate.
Electronic organs and pianos can play them too! The new ones have USB slots but I still remember the old ones that had floppy drives.