I guess it does depend on the company. When I read your post, I was upset thinking how a company can act so unprofessionally. But as I was reading the other comments, I kind'a started thinking... There are actually two sides to it.
Firstly, how a company treats their potential employees shows (or at least makes one wonder) how they would treat their employees. Making a candidate wait for 3 or 4 hours for an interview shows complete disregard and disrespect to the candidate's time and personal needs. I may have an emergency doc's appointment at 4 and would've thought I will attend my interview (because I need that job) from 1 to 2, and go to the doc. But because of the wait, I miss my doc's appointment. I may be a diabetic who requires food or medication every hour or two hours. Any number of such situations could happen. It is important to keep an appointment. If you cannot due to a last minute emergency, then make arrangements for an alternative interviewer or contact the interviewee, apologize for having to reschedule the interview, and set up a different time, before the interviewee shows up.
Secondly, how an interviewee takes this whole wait thing, I suppose, also depends on how the company treats the interviewee during wait time. Allowing the interviewee to socialize with the employees shows trust – we trust our employees to give you a good feeling about the company. We trust you to be a positive force among our employees, learn about our work life, and how we are with each other on a day-to-day basis. After all, if you are selected in this interview, you will be one of us. Letting the interviewee participate in such activities (not some math exercises or quizzes etc., but real) “a day at our company being an employee” kind of activities (nothing company confidential, but very general) would make the interviewee not mind the wait – because then (s)he is not waiting. It would be a part of the interview process – because, you can also analyze if he/she is a good cultural fit in your company. In this case, regardless of how the “actual” interview goes, the candidate will take away a good feeling about the company.
Just sharing my thoughts.
Thanks,
--Som G