On the USofAn / European cultural difference in perspective: there's also a rule of thumb here in the US that some people stay "plugged in" to the office while on vacation because their bosses and coworkers have made them feel that things at the office will suffer if they're unreachable while they're gone, while some people stay "plugged in" because they're afraid that their bosses and coworkers will find out that things don't in fact suffer if they're unreachable while they're gone. All of which is to say, some really are indispensable; many others just hope they are.