He's also ignoring the fact that if your job's responsibilities are mission-critical, chances are you have a contract which stipulates situations in which you can be contacted after hours. It's about Joe Schmoe IT guy being called in at 7pm while he's having dinner with his family and being told to come to work because Greg the assistant to the Sales VP forgot his password again. Greg can fuck right off until tomorrow morning.
The server going down at 2am is mission-critical and the guy in charge of it will definitely be answering that call to fix it.