Think of this as an old time player piano.

The piano itself actually plays the sounds that you hear. The cartridge roll that you put in the player piano contains information that tells the player piano what notes to play, when to play them, and how long to play them. In that analogy, MIDI is like the cartridge roll of a player piano and EZdrummer/S2 (or any virtual instrument) is the piano. This is what makes virtual instruments and MIDI so powerful. You can create your part with MIDI and change it later. I’ve created a virtual violin part before and then, later, changed it to a cello. The MIDI and the playback sounds aren’t tied to one another. You can play a MIDI grand piano sound and then change it to a funky tack upright after. Impossible to do with audio without recording the part again. With MIDI, it’s easy.

MIDI loops are different than audio loops. With MIDI (and you host sequencer) you have the ability to change anything and everything about that MIDI loop. In regards to MIDI drums, you can turn a snare hit into a cymbal hit, you can totally the kick drum pattern, you can copy the hi hat pattern from inside one MIDI loop and use it inside another MIDI loop. With audio loops, you are limited to what you can do with it. You can change the tempo by time stretching but you can’t change what that audio loop is doing in terms of what the kit pieces are doing. You can do some creative chopping of an audio loop (stuttering effects, etc.) but what is there is there.