Velvet Dress is "too slow" as well, and the band played it anyway.
"Lemon" and "Numb" are studio pieces and the band found a way to present it live and to insert (and make i fit) it on a show that had already a concept previously conceived.
These are no excuses.
To be perfectly honest, I think your analogies fall flat, in fact, they serve to further support the belief that the songs that are being left out should be left out.
Velvet Dress is a sultry sexy tune, it's supposed to be slow groove song. These sorts of things typically work wonders on female audience members.
Lemon has a chorus, a complete song structure and Bono doing some of his best falsetto. Also, it's catchy, was generally known (I mean, it's found at Karaoke bars, for chrissakes), generally infectious, and worked well live.
Numb features Edge doing lead vocals, and a rap - and - wait for it - a CHORUS!! Unique, awesome, and about a million times better than Fez. It translated very well live, also.
Also, just to get you thinking on something...when U2 writes, enters the studio and records, they are artists. When they conceptualize the tour, the stage, the lighting, the graphics, etc, they are artists, first and foremost.
When they hit the stage tonight, there is a distinction. They are performers, first and foremost. They are performing for an audience that has paid to see them. There is indeed a necessary catering to the audience that goes on, and it in no way diminishes their artistry or otherwise invalidates them as artists.