There are big differences. Most gardens in the UK are quite enclosed (often they have around 2m high brick or stone fences and they're not very big usually either). Also there are pretty much no natural predators for cats here (apart from humans I guess) and because most cats go outside it's assumed that any cat you run into outside that seems healthy is a cherished pet.
That means that random people stealing or hurting cats is probably more rare than when it's assumed that an outside cat is a stray or feral.
In addition to that cats are protected by "free spirit" laws in the UK. Basically they're legally recognized as a free spirit that can't be controlled so the owner is not legally responsible for any damages a cat may cause. I.e the potential legal liability for a free roaming pet cat is zero. Not that most people worry about that.
I've just had a discussion with my vet about inside/outside cats and she said that the live expectancy was about the same although slightly less for cats that went outside but not by that much. Most of her oldest patients went outside. However behavioural problems were much more common in indoor cats and a lot of behavioural issues were practically unheard of in cats that went outside and one of the first suggestions she brought to me when I was having an overgrooming problem in Nikita was if I could possibly let her go outside since that has solved the problem with other cats in the past (it has after that turned out to most likely be allergies rather than behavioural overgrooming though)
However it's perfectly possible keeping cats happy indoors, it's just involves quite a bit of work sometimes, especially if the cat is a single cat. Same with going outdoors, it depends on the situation. Sometimes it's really not safe and sometimes it's safe enough. It's never 100% safe but then again nothing is.
Edit: Also for example here is a map of the city I live in (just a part of it and not where I live). You can see how the houses are built together and completely enclose the garden areas behind them. There is no way a cat that is let out into that area will be run over by a car.http://maps.google.com/?ie=UTF8&t=h&...,0.004689&z=18
In addition to that there are fences and stone walls within the green area to mark off which bit of garden belongs to what house.