Are you replying as their hired Pro (If they have one) or as a paying punter?
I have taken my DSLR to many concerts before, but always read the small print before hand, and sound if I'm allowed. Darren, I'm not trying to take away from paid pro's, but I know you know the difference in IQ and results in general between P&S and DSLR.
Is it fair, sure it is, I'm not getting paid to shoot the show, I wan't some for personal keeps. If I was getting paid for it, I'd be wearing a 'Getty' badge and getting plenty for it.