In the U.S. this is how employees work as well -- they can leave a company for any reason at any time. Conversely, employers can dismiss at employee for any reason and at any time as long as it's not illegal.
It's a double edged sword. It's easy to be let go (basically, pack your stuff and get out while escorted by security, just like in the movies), but it also makes it much easier for companies to take a risk and hire you. In Europe, hiring someone is a big risk and companies are extremely careful to hire since they're taking on a big responsibility. As a result, permanently contracted positions are even more common in Europe than the US as a result in my experience.