It's true that some other genres of music do rely on books a lot more, but we're talking about much longer and more complicated works than a 4-verse song. If you're singing Bach's St Matthew Passion, you've got a big fat score that will take a couple of hours or more to get through, and no one expects choirs to do that from memory. Even the parts where you don't sing need to be followed in the score so that you know where to come in again (there's probably only been one run-through with orchestra and soloists). Even church choirs may have several different hymns/anthems for every church service. Another reason that choirs have scores is that they all have to sing it exactly as written - not only the words and the notes, but the dynamics and speed-changes, breathing points, etc, some of which will have been pencilled in for this particular performance. Some conductors won't let choirs sing from memory, as they want everyone to have the last-minute notes on the interpretation in front of them.

Classical soloists often sing from memory, or without much reliance on a book. Pop singers don't sing from books, and neither do country, blues or jazz singers, adn our material is no more difficlut thah theirs.

One final point to consider: you say your memory isn't what it was, but your eyesight is probably diminishing at a similar rate. If you rely on books of words, you may soon find you can't read them in certain lights - it's much safer to put in a bit of work and get the song in your head!

Marje