You're probably right, dmg. Another problem was that, on occasions, the comedians seemed more intent on addressing the TV cameras (and thus the TV audience) rather than the audience around the stage. This caused a "disconnect" in a live situation.
Also, each comedic segment was so short that the comedians didn't have the opportunity to build a line of humorous comment up to a really funny punchline. AS professionals, they should have realised this and adjusted their material accordingly.
Even Lee Mack seemed unable to "connect ". He can be incredibly quick, sharp and witty on a TV game show and not too bad a stand-up comedian, based on the few occasions I've seen him on TV, but none of that came across.
Most of the comedians in the concert seemed to want to be "clever" (or "smartarse"), failing to recognise that they were not performing to their regular audience and failing to recognise that a concert setting like that is different from what they're used to. This crowd came for a music concert and for the Diamond Jubilee event, not for a night out with comedians. They didn't make me proud to be British - I cringed most of the time they were on.