They aren't only like this from inbreeding, this happens in the wild.
Some cats carry a special 'white gene' and if both parents have it, the offspring will be white. It is a mutation. More cats have it in captivity than in the wild, but it can occur in the wild. It's like albinism but only the orange part of the fur is white (they aren't related, both mutations, but they both involve color in the fur and melanin and such). In some cases the stripes can be white too.
There are also 'golden tigers', which have orange fur and darker orange stripes. They look pretty cool, but there aren't many of them I believe.
While white tigers are pretty, I think inbreeding them to be like that is wrong. If a tiger is born naturally like that in a zoo, that's cool. But selectively breeding them so they turn out white for zoos? That's not right, even if it is just fur color.