I've heard it far too many times. The Stand and Swan Song are nearly the same. So... for my next three books I will read and compare not just The Stand and Swan Song I'm throwing Dark Advent by Brian Hodge into the mix as well. It's compared to The Stand far too often.
BTW I can think of only two similarities off hand.
Similarity the First: The Holland Tunnel is traveled through in both.
Similarity the Second: Randal Flagg and The Man with the Scarlet Eye are both evil and possibly demons, both vanish from the story in the same way and appear later in the story.