Many folks have asked the same question. Due to external pressure from the movie industry, most hardware manufacturers have protection built in to their firmware in order to prevent "free region changing". At least for those devices sold or used in the US and Canada.
My personal opinion is if you legally purchased the DVD movie you should be able to play it without having to change region code. Generally, the region code can be changed five times before it defaults to the last one used.
Send me a private email if you wish to have the link for firmware updates. NOTE Updating or replacing firmware using a non Apple provided firmware update will void the warranty on the drive and may actually render the drive useless.