Tech firms that offer lavish perks to their staff do not do so out of the goodness of their hearts. They offer them because they expect people to work so hard that they will not have time for such mundane things as buying lunch or popping to the dry-cleaners. […] Some of the most extravagant perks are illusions: “take as much holiday as you like” may really mean “take as little as possible, and as much as you dare.”