It is actually rare that prospective employees have an open account but when it is open and accessible to the public, then permission is implied for ANYONE to view the contents of the page including employers. I certainly don't ask for passwords or view private information, only what people have left open to public view. It can be very revealing. It should not be offensive to you, you should just ensure that your facebook page remains closed to anyone who is not your friend, especially while looking for a job.
I am an employer for a small business and can not afford to waste time and money training employees only to find out they are not at all what they portrayed themselves to be in the interview. If simply checking a facebook page gives me information about someone that would make me not want to hire them then it saves time and money and it is worth the 2 minutes it takes to check. I have only given this information on this site so that those seeking employment in a highly competitive market can learn how to best present themselves. It does not take much to change the settings on a Facebook page, and it could be the difference in whether or not you get a job.
(I absolutely do not believe employers should have access to Facebook passwords or any other private social networking information.)
neelieyelik: As an employer I always give a return call or letter to every one of the people who have been invited to an interview as soon as the decision has been made and the new employee has agreed to be hired. I believe if I have asked you to take the time to get dressed up, stress out about what you are going to say and how you are going to present yourself, drive to the appointment, wait for me to be ready for you etc... then at the very least I can call you back whether you got the job or not. I am sorry that you have had that experience. I think it should be a priority for employers, but I also work in small business and make it a priority when going through the hiring process.