I've had four cats in my lifetime, and all four were indoor cats. They all lived long, healthy lives. One of them always tried to sneak out, but finally was willing to let me put a harness & leash on her, so she could go out and explore the garden for a while. My last cat lived to be 20, but was rather deaf by then. Since she was the only cat in the house, she seemed to take it in stride.

One other cat that stayed around the house for a while (an un-neutered Tom) was always getting into fights. I took him to the vet many times to get patched up after he got into fights. One day he just never came home, and we never found out what happened to him.

As for the difference between UK & US, I hadn't thought about that, but it makes sense.