The Earpiece Conspiracy...

I know that most singers have an earpiece while doing live shows.
What exactly is the purpose of it?  I was at last nights show in 'DC
and noticed that Brian was having a hard time with his earpiece and
the roadie kept trying to fix it inbetween songs.  I thought it was
pretty messed up that the rest of the band clearly noticed Brian and
the roadie ru****ng like crazy to fix whatever was wrong but they
seemed completely indifferent to his problem.  They just kept starting
the next song if he was ready or not.  All I kept thinking was why not
wait 1-2 mins and let them fix whatever was wrong?  Before STT Brian
just ripped the thing out and sang without it and is clearly out of
tune as a result: http://www.youtube.com/watch?v=By9bbXOQp2w

My questions are;

1-What the hell is that earpiece for?

2-Why wouldn't the band give them time to fix the damn thing?

On another note when the roadie finally fixed the thing Brian gave him
a high 5 and was clearly very grateful, very nice to watch.

The show was amazing, the band was tight, loud and not slopply at
all.  Angus gave it 110%, I was pleasently surprised at his
performance despite some earlier undeserved posts.  He can still play
with the best of them.  Funny thing was that he tried to get his hat
to come off during HAABPTB but it wouldn't and he just played with it
on for like 3 more songs than usual.

Brian sounded awesome, powerful and he didn't seem to lose steam at
all, with the only problem I noticed with his earpiece fiasco.  I also
thought that he might have hurt himself trying to swing on the bell,
when he came down he kept grabbing his groin and had a painful look on
his face.  For gods sake please tell Brian to stop doing that, no man
at 61 has any business swinging on ropes in mid air.

I brought my brother-in-law with with me.  It was his first AC/DC show
and he was amazed.  He kept saying "how the hell do these guys have
the energy to perform like this at their age?"  He was shocked when I
told him Brian was 61.

This was my second show of the tour and I noticed that BI is the least
received song, being when most people hit the restrooms/beer line.