Bacteria like Salmonella survives and reproduces best in alkaline conditions. Cats have short acidic digestive systems which means the food passes through their systems quicker than humans and even dogs. Food, especially raw meat, doesn't sit around in the cats system long, so combined with acidity level, bacteria doesn't have time to reproduce.

Here's a couple of links with some good info on raw feeding cats:

What About Cats?
Feline Future Nutrition Reference - understanding cat food