It's not they don't sing live at all, they do, and more than what we get to hear. (I never attended a concert but I listened to some audio recordings) But then JE edit the audio for the DVD. If you go and watch the cuts aired during Shonen Club Works, which are taken from the same date of the DVD, you can hear that 5x10 was live, but in the DVD they edited it, it's a shame! ç_ç

That said, all the solos except Nino's -and I think most probably Sho's- were playback from the start.