Perhaps you saw this article in the Friday Washington Post detailing the staggering number of emails missing from White House electronic archives. The post article does not make this clear, so Scott Horton points us to the CREW report which details from what offices and around what time periods those emails are missing. Unsurprisingly, they are missing for time periods when investigators would most interested in seeing what any emails might contain. Coincidence? I doubt that very much.
UPDATE: Additionally, if your system is designed to be inept, you can handily claim mere incompetence to disguise what is actually the deliberate deletion or failure to preserve e-mail records.