MIDI does not have a sound. It's just instrument data. The classic "MIDI sound" that you recognize is the Roland GM soundkit shipped with Windows (an early version of Roland's Virtual Sound Canvas product).
This website uses a different instrument set. You can actually select which one it uses in the Settings panel, but by default it uses Kenneth Rundt's GMGSx.sf2 (which does sound quite a bit Roland-y to me), as shipped by SynthFont.
I don't know what instrument collection GarageBand uses.
This website uses a different instrument set. You can actually select which one it uses in the Settings panel, but by default it uses Kenneth Rundt's GMGSx.sf2 (which does sound quite a bit Roland-y to me), as shipped by SynthFont.
I don't know what instrument collection GarageBand uses.