Perhaps the main reason why many more cats in America of full-time indoors is because there are more predators in America who would kill a cat. But it goes beyond that and because there are so many indoor cats in America it is one reason why there is declawing in America because the argument goes that cats don't need their claws if they're indoors all the time.
Using that argument, some Americans might believe that British people don't declaw their cats because they let their cats go outside unsupervised and therefore they realise that they need their claws to defend themselves. This is incorrect.
Cat on UK road. I don't like to see this because I have experienced cats being killed on roads.
The reason why British people let their cats go outdoors and why nearly all cats in the UK are indoor/outdoor cats is because British cat owners want their cats to live as natural a life as possible and they are prepared to let their cats take the risk of being injured. The biggest risk of being injured in the UK is by a vehicle on the roads.
In the UK, many people don't know what declawing is because they had never heard about it and it does not enter their minds. It is not part of the equation. It's not part of cat caretaking in the UK. Therefore, the declawing of cats has no impact whatsoever on decision-making about any aspect of cat ownership in the UK.
It could be argued that many British people are too sloppy and laissez-faire about letting their cats go outside. I could accept that argument because I believe that if cats in Britain are allowed to go outside they should be supervised or the area where the cat lives should be safe from potential road traffic accidents. That is not always the case.
Whereas a British person might criticise an American person for keeping her cat inside all the time, an American person could be justified in criticising a British person for letting her cat go outside unsupervised where it might be unsafe to do so because a road traffic nearby. Sometimes, a middle ground is probably the best balance between safety and a natural life.
Some Brits have never experienced the loss of a cat on the roads. If they did they would not be so relaxed about letting their cats roam.
There may come a time in Britain when more people follow the American lead and keep their cats inside full-time as the population of the UK increases resulting in more traffic and therefore more risk of injury for a cat.
If you are a Brit you may have a different viewpoint. If so please leave a comment.