ONLY if we assume the way we treat commoners know is supposed to be 100% based on historical evidence. Personally I've always gone with the "Tom would like to see it this way" approach.
Tom generally knows more about this stuff than most BM players do, but he has been amenable to changes (or, at least, not come down on people who behaved differently) when you present him with historical evidence. General rule of thumb for something out of the ordinary is if you can present two (properly cited) historical instances of something, that's good enough to justify it.
I personally think it would be awesome to have some realms have slaves working the fields, others with more standard villeins, still others with lease-holder farmers, and have wars start because the slave-holders don't like that the people next door let their farmers lease the land.
