Bars lose about 24-26% of their gross revenue to theft [1]. Further, bars are about customer service and every bar has a GM or owner who is there most of the time monitoring their employees. Adding cameras only allows them to do it remotely, it doesn't change the fact that they are watching.
The fact is that bartenders are mostly paid in tips and handle a lot of cash (some bars can pull in $60K/week gross). Not only is there a lot of opportunity, but frankly, most bartenders aren't paid very well. Combine this with lax monitoring and you are asking for theft.
Show me an office that has that kind of theft and I'll happily recommend monitoring there too.
[1] According to Bevinco (they do auditing of bars/nightclubs by doing things like weighing bottles at the end of the night and comparing it against the POS) - http://www.nightclub.com/bar-management/employee-theft/thwar...