No matter which side of the indoor/outdoor cat debate you fall on, it's important to remember that all cats need attention and stimulation. Cats are so autonomous and independent that it's easy to forget that they do need us, no matter how indifferent to us they may seem.
Outdoor cats may get plenty of stimulation, action and maybe food and water, but they still need love. In our area, it's a good idea to bring them in at night to protect them from coyotes, too. We had a sad period in our neighborhood a few years ago when there were several different missing cat posters everywhere. Luckily, coyotes are wanderers, but they do come back.
Indoor cats may get plenty of love and have food and water at their disposal, but it's easy to forget to stimulate them with playtime. They may have a safer life indoors, but we must make sure it's a quality life. Even older cats may have a few bats at a swinging toy.