When I was a kid going to church I sometimes closed my hymn book during a hymn, just to show off the fact that I'd sung those words to that tune so many times that I knew them both backwards. Now, my memory is good, but it's not superhuman, and most of the congregation at those services had been singing those same hymns for a lot longer than I had. At a conservative estimate, half the people there knew the hymns just as well as I did - and yet they still went through the motions of opening the book and finding the right page. I imagine this was partly in case they did forget a word, partly because it was what everyone else was doing, but mainly because they'd been doing it for so long that not doing it would seem snotty and ostentatious.

I think something similar is going on when the Coppers use their book. Put it another way, hands up everyone who thinks Bob Copper didn't know Thousands Or More by heart. Where the Coppers are concerned there's the part-singing element as well - from my limited experience it's much easier to get a harmony line right if you've got the dots in front of you.

What kind of message are you giving out if you sit there saying"I can't even be bothered to try to learn one song"?

I've seen some very good singers use words as a safety-net. Blanking in mid-song is horrific, and can strike unpredictably - back when I used to do covers, I once did Nick Drake's Which Will for a floor spot on the spur of the moment, and blanked between verse 1 and verse 2 (the entire song is eight lines long). There is some overlap between "good singer" and "has songsheet". But there's a much bigger overlap between "has song folder/notebook/ringbinder" and "bad singer".