I think it changes. It's a bit of a grey area when it comes to where the line is. A direct supervisor asking out an employee, in my view, is totally inappropriate. Someone of a higher rank asking out someone at a lower rank who works in a totally different area of the organization, that is just human nature, but if the individual knows it's unwelcome, then it better stop quick.
On April 18th, 2013. See this statement in context.