If people don't think it would work for them, don't do it! It works for us because I can't afford to spend a fortune, it stops us falling into the realms of what does DS1 buy DS2 and DD1 and DD2 etc, we all help plan each other's gifts but it doesn't end up plunging me into debt which buying 12 different presents just from the kids to each other plus a mountain of other stuff might well do! I have no judgement whatsoever if people choose to do this and spend a lot and give a lot of gifts. I cannot afford to (and yes I am probably more than a little jealous of people who can buy mountains of gifts for their kids...!)
Want is the big present. Need can be anything - last year I got DS1 a scientific calculator as his "need" which was his favourite present. DD2 got a Hello Kitty lunchbox as her old one was tatty. They like these things! I wouldn't buy something for them just for the sake of sticking to the rhyme, I quite enjoy the challenge of finding things I know they will love in each category. And "need" can be subjective ;) I could say I want a new pair of shoes, I need a new pair of shoes. And I wear a new pair of shoes. That's three new pairs of shoes, yay, best Christmas ever!
Someone up thread asked what if someone wants five presents. I'm not sure I understand - what if someone wants twenty presents?! We have to draw the line somewhere. This works to do that, it helps manage the kids expectations too. If someone wants five presents, well, they don't get five! They get four. We all get four.
We also have a lovely lunch together, we pull crackers, we watch Christmas telly, we drink wine (those of us over 16!) we see family, we play games. Presents are brilliant but it isn't just about the presents for us.
As I said, it works for us, it wouldn't work for everyone, and that's fine :)