updated 04:57 pm EDT, Tue May 14, 2013
Apple discourages complicated requests
Apple has run a server-side update to Siri, changing how the service responds to long commands, notes iLounge. If Siri judges that a request is too long, it will now reply with a quote from either William Strunk or Thomas Jefferson, in either case praising brevity of language. It's not clear exactly when the update was made, but it appears to have happened during the last week and a half.
Although Siri is marketed as a built-in component of iOS, in reality the feature won't work without a connection to Apple's servers, where the actual interpretation of commands happens. This does however allow Apple to improve Siri without updating iOS, which could take substantially longer. The need to discourage lengthy commands suggests that Apple's voice recognition system still has trouble deciphering complex phrases.