The Netherlands does not have any native wildlife that is a threat to cats, nor do we have nasty diseases like rabies (there have been no domestic rabies cases in the Netherlands for over 50 years now, all cases we did have were tourists that got bitten in some foreign country).
I disagree on indoor being healthier for a cat over here. In my experience, indoor cats live up to 12-15 years of age, usually dying of hearth or kidney problems (overfeeding and/or lack of excercise does that), and have a tendency to grow lazy and fat.
All my family's outdoor cats (with the exception of one that got run over by a car) passed 20. Hell, my dad had a cat that lived up to 29-30, and all but the last year of it's life it happily roamed outside. My oldest 3 cats are 12 now, and they're lean, muscular and fit as a feline should be.
Now I'm not one of those guys that will tell you keeping a cat indoors is cruel in all circumstances. If you raise a kitten in an indoor environment, it can be perfectly happy, not knowing what it misses out on, and I can perfectly understand that if you live in bear/badger/wolf country, it could very well be the safest bet.
But cats like mine that have known nothing but being free to go where they want for all their life, you can't turn those into indoor cats. They'll turn neurotic and sad.
EDIT: looks like Google is pretty much wrong then about Dutch wildlife.
let's see... Foxes? Extremely rare. Won't find in cities like you can in the UK. Not a threat to city cats.
Wolves? Nope. Once every few years a German or Polish tourists pulls off a stunt, and drops a dead wolf on Dutch roads. Then the nature freaks all go hype 'THE WOLF HAS RETURNED TO THE NETHERLANDS AFTER BEING EXTINCT FOR 2 CENTURIES', only to come to the conclusion after genetic testing that it's a hoax wolf from Poland.
Bears? Lol, just no. There's no bears in the Netherlands. Don't think there have been for at least 1000 years.
Badgers? If you see one, call the newspaper. They're either extinct or maybe there's one breeding pair still hiding somewhere under a rock in the National Park de Hooge Veluwe.
Beavers? Okay, we have some that were released back into the wild about 20 years ago, and that turned out to be a really succesful project. Water management is even starting to ask permission to cull their populations, because their dams threaten our water management. They're nowhere near where I live though.
Hawks? We have some small birds of prey, they're pretty darn rare, and even the largest one is nowhere near large enough to tackle a cat.