Some myths I've never heard of before. But yeah, it just proof again that you should never take something on face value (especially on the internet) - maybe some of his stuff needs to be checked too, who knows and who has the time?! On a side note, the guy's voice will drive me crazy if I have to listen to another one of his lists!
Speaking of cleaning habits:
The best/simplest advice I've come across was that human nature hasn't changed all that much. It rang pretty accurate to me. So just like today you get people that bath twice a day to people that don't bath that often, you'd get them back in the day too. Granted, running a bath was a b#tch those days, but that's about the biggest difference (and might at most changed the twice a day person to a once a day person, maybe, even then, if you ever roughed it, you know you can do wonders with a bucket of cold/luke/warm-if-you're-lucky water and a cloth).
The old tribes in Africa had really good teeth for people that didn't have fluoride toothpaste. Reason why - they sat for hours a day cleaning their teeth with sharp sticks. It was time consuming, but worked just as well if not better.
Also, I'm sure that if riders ran out of ale/wine, they would drink water from the streams. So some might have taken a liking to it too, who knows. But only a few probably, with that much beer around, who'd prefer water?! LOL Side note, one of these days Amy will be able to tell us how much beer $50 of TNBW prize money can buy! No pressure Ames!
And then this ... slightly different reason for not taking a bath, but related to the topic of bathing:
http://www.news.com.au/lifestyle/beauty … 7519995565
So who's with me?! No more bathing. Yay!!! 
But yeah, my characters bath and wipe and clean themselves. If they didn't ... *shudders, I'd probably never read or write a historical romance novel ever again*