Simple ideas?

I've just finished reading The Permaculture Way by Graham Bell and found it extremely interesting - although not easy to suddenly change your life to this way of living - I think any change for me will be gradual. I know that I would lose my allotment if I didn't keep it neat & tidy and free from weeds - although the idea of no weeding is very appealing - they seem to grow so quickly, if only my vegetables would do as well! One idea that has stuck in my mind though is why do parks authorities plant ornamental trees rather than fruit trees? Apparently they say people will take the fruit - isn't that the idea?