This is how a job should be. You get paid for doing a specified number of hours at something you are good at. You don't get promoted to your level of incompetence, and the company doesn't sneakily steal hours of your personal time away.
This is why I think it's essential to have one GTD system for work and one for non-work. For the job you are talking about it enables you to focus all your attention on the job without being distracted by things you have to do at home. For the 99% of other jobs it enables you to switch off from work when not at work, despite the guilt that most organisations' cultures use to control their employees, making them feel like they need to work more than the hours specified by their contract.
The more in control you are in your job, the more confidence you have to refuse extra hours arbritrarily demanded by others in the organisation. Also, the more confidence you have to change your job, if there is no other way.