Most jobs I've ever had in the UK came with a "probation" period of 6 months, where the employer could terminate the position with a one week notice (or even shorter if I was the cause of some particularly nasty problem), and after 6 months a review would be conducted to decide if the position was going to be offered on a more permanent basis.
I think it's only fair that employees can have the same option to walk away if they find they don't really fit in the culture of the organisation.