a.) I don't think that's necessarily true.
b.) Again - I don't think anyone is looking that deeply into it except for actual U2 fans. You stated earlier that "if they know the band enough though to listen to them and compare tracks from each album I think they’d be aware of the album titles as well." But that's the point - no one's comparing tracks except for us. They're just listening to the new album on New Music Friday. I'm sure there's a large amount of listeners who listened to 13, heard "there is a light..." and didn't even think of Song For Someone.
As an example: I'm a very casual Red Hot Chili Peppers fan. I listen to the new albums when they come out, but I don't frequent any message boards or dive into the back catalogue because I just don't care that much. I like them, but I'm not a diehard.
They dropped a new album last week that was a companion piece to their last album. If, hypothetically, this companion album was thematically linked to the last one and they'd repeated lyrics to drive home the theme (they didn't), I'd have *no idea.* I just put the albums on, listen, save the songs I like, and never think about the other ones again.