Easy -- Staggered layoffs.
http://humanresources.about.com/od/glossaryw/qt/WARN_Act.htm
Even at BMC, people are being let go in stages. Very few people left in the initial wave. As long as they don't layoff X number of people in a 30 day period, they don't have to abide by the act. That said, you know BMC is teaching out. If you think the others aren't on the block, you are probably fooling yourself. If EDMC as a company is around in 3 years, I will be shocked.