bostonidealist's Journal: Simultaneous SSL Expirations?

Over the past several days, Slashdot, T-Mobile, Oracle, and Apple have all had expired SSL certificates that have impacted services (several of these issues have since been fixed). Why are there so many synchronized, high-profile lapses? Is it just a coincidence, perhaps related to the Memorial Day holiday in the US, or is something going on? Was there some sale on certificates some time ago that caused all these companies to renew (and subsequently expire) their certs at the same time?