Originally posted by RattleandHum1988:[..]
I think the difference is that Summer of Love existed as a piece of music before even being brought to U2. It wasn't a riff that someone came up with during a U2 session, in trying to make a U2 song better (which is sort of what a producer is there for) - it was a part they came up with during a One Republic session, that Ryan Tedder brought to U2.
But yeah, I'm pretty sure that one studio scene in From The Sky Down basically confirms that Lanois came up with that main guitar part for One (although, he didn't come up with the basic music - the chord structure, etc.), U2 did that themselves.