"Normal" is in the eye of the beholder, J. ALW has more mainstream appeal (or had, at least) because his melodies sound vaguely like songs you've heard before. They're familiar, and therefore comforting. Sondheim's melodies move in ways you don't expect, but ways that are beautiful nonetheless. They challenge the ear and expand it. Some people find that unpleasant. They'd rather listen to "normal" music- to the same old thing- their entire lives. They're missing out. ALW is good, but Sondheim is brilliant.
And to get back on topic (sorta), Joanna Gleason rocks my socks on the OBC of
Into the Woods. Her delivery of "If the end is right/ It justifies the beans!" cracks me up every time.