[manarth]

The main difference is high-pressure water (espresso/keurig) vs low pressure water (drip coffee). They taste very different (e.g. whiskey vs beer).

You could even argue that there's less waste in espresso-style…people make a single drink at a time, and generally drink it. With large carafes of drip coffee, a lot gets thrown away because sitting too long on a hot plate causes it to taste burnt.