This is good, because in an era when ever more people are choosing (or having) to living in high-density small-apartment boxes in high-rise towers, an indoor only rule would be bad news for cats.
The dominant sense for us humans is sight, but cats live in a 70% smell-world. Scents are vital to their brains and pleasure states -- scents that waft on the breeze, hide in soil and bark, and are left as markings by other animals. The scent of carpets and upholstery just doesn't work for them. Nor do they want to miss rolling on the grass, climbing trees, stretching out in the shade of a bush, clocking the movements of other cats or walking up to neighbours for an ear-scratch.
Indoor cats suffer constipation, poor digestion, poor muscle tone, arthritis, snagging claws, obesity and boredom.
Cat-jailers talk as if all a cat in the garden thinks about is having wild sex and hunting mice. Mine do neither; get them neutered and feed them well, and neither will yours. A cat being left outside to shiver in the cold is of course just as sad as one being imprisoned on a hot well-scented day. The key is moderation, consideration and common sense.
The SPCA suggests hiding food around the house so your cat can "stalk" it as entertainment. My suggestion is that cat-jailers buy a fluffy stuffed animal and some pretend-food, and entertain themselves by "feeding" it to their "pet." If a stuffed toy is what they want their living cat to be, maybe they should just buy one, and let someone else adopt the cats.
The SPCA contacted Animal Literature to clarify their position further: "The only circumstance in which we would turn down an adoption regarding an outdoor cat is if the potential guardian is not planning to provide food or veterinary care for the cat - sometimes people want barn or field cats but our policy is that the individual must provide food, veterinary care and any other needs of the animal, even if they are outdoors.... Whether a cat is indoors or has some outdoor time, it is our responsibility as humane communities to ensure they they do not suffer." For sure we can all agree with that.