I don't really hear Somewhere That's Green and Part Of Your World, beyond how they generally relate to all that guy's balladish songs.
NYLG, you're right, they are similiar melodies, although I like "Happiness" better and it soon takes off in a different direction from the other song.
I dunno. There are only so many notes and combinations of notes, and a composer with a long career is bound to start copying his or herself.
A funny Sondheim one my friend pointed out to me. I thought she was crazy, but she told me she thought some random part of Assassins was ripped off from some random part of Into the Woods. She thought it was in the song "Another National Anthem" but she wasn't sure about which part of Into the Woods it was. I listened to the song and determined that the bits of the melody that go like this:
"There are prizes all around you if you're wise enough to see. The delivery boy's on wall street and the usherette's a rock star!"
Wherever it does that in the song reminded me of:
"We can't sit around and dither while her withers wither with her."
Apparently that's exactly what she was thinking of. I'm sure he's used that little bump de dump like 5 million times but I think it was a pretty random thing to notice!
yr ronin,
joey