Hazarding a deductive guess at the relevant etymology of that phrase john of MT, I'd say it's because like a G Em C D verse with C D G Em chorus in common with C Am F G verse and F G C Am chorus, they're both simple, easy to play, ubiquitious progressions which like ice cream are essentially the same product which can be represented in multitude of different flavours which almost [u]everyone[/u] (the lay ear) loves.