The smartphones and remote access technologies are also convenience for the employee, to enable balance between work and life. It used to be that if we needed to do something out of office hours, we had to go in to the office. Long hours meant being at the desk, same with weekend work. Technology has changed how on-call work takes place; instead of shifts at a desk, you are expected to be reachable. As long as there is compensation, okay.
For vacation, people should switch off, except for rare exceptions. People need time to recharge, get out, smell the flowers. The company benefits from that too - new energy, new thinking. In addition, in some jobs, it's actually good for a company to demonstrate they don't overly rely on a single person. Don't want to find that out the hard way that someone is the only one with the passwords or keys, knows where crap is, etc.
In fact, some jobs have a mandatory block leave for regulatory purposes. Ie securities trading, etc. Staff need to be off for a continuous one or two week period, and companies often yank their access in that period, to show that one person does not have undue control.