Yep singles are not important in terms of sales but I remember when Boots came out and all my friends were sending me messages saying "what do you think of the new U2 song?? I not so sure ??" or "I heard the new U2 song - didn't think much to it" - so to non-U2 fans the first single from a new album is very important since it automatically gets lots of radio airplay.
Also remember U2 got an *amazing* amount of publicity when they played the Grammy and Brit awards as the opening slot.... as well as other TV appearances.
"However, it [Boots] underperformed in comparison with earlier lead singles from U2’s studio albums, peaking at #12 in the UK Singles Chart and making it the first lead traditional format single by the band prior to its parent album release to fail to reach #1 since "With or Without You" in 1987, the first lead single to miss the Top 10 since "Gloria" in 1981, and the worst debut for a U2 single since "If God Will Send His Angels" in 1997. It also broke a string of 14 consecutive UK Top 5 singles for U2. "
As for MAG:
"Magnificent" debuted at #42 on the UK Singles Chart, becoming U2's first domestically-released single to completely miss the UK Top 40 since 1982's "A Celebration" peaked at #47."....
I wonder what U2 and Paul McGuiness thought about that !