Is it possible that the breached Sony passwords he was analyzing may have been cracked with dictionary attacks? Maybe the reason only 1% of the passwords had a non-alphanumeric character was that the crackers mostly didn't crack the passwords that had any non-alphanumeric characters.
"The science of password selection" (a breakdown of common passwords by selection practices, as taken from public leaks)
http://www.troyhunt.com/2011/07/science-of-password-selectio...
In short, passwords are chosen from:
People names: this includes a list of about 26,000 common first and last names.
Place names: this is everything from towns to states to countries and includes about 32,000 entries.
English dictionary
The most common passwords by group:
Name:
Place: Dictionary Words: Numbers: