Well, to be honest, that is fairly typical of high risk layoffs. Companies are rightly concerned about sabotage and other retaliation. I worked at a computer company that didn't do this and announced layoffs in advance. They regretted it. I also knew people who were part of a mass lay off from a major online company and they were taken to an offsite meeting for the announcement and not allowed back to the office. The company packed up and shipped their personal belongings to them.