Regarding Bono, I believe the idea is to position the mics so that your only singing into one. Perhaps they are staggered by an inch or two. BTW, in the 1970s, there were live mic rigs that had a similar principal, so that the PA could be behind the band w/o the mic feeding back. The Dead's "Wall of Sound" employed this, for example.
William, two questions:
What's the phase cancellation like, if any, when you mono sum the piano with that technique?
And those wall hangings: Is that a real poncho or a Sears poncho? Hmmmm. No foolin'?