There's a statement on http://www.w3schools.com/tags/att_td_char.asp, a w3cschools page with a 2012 copyright (though that may be a mere boiler-plate footer) that "The char attribute is not supported by any of the major browsers."

My guess is that has more to do with reproducing their results than your doctype setting. When I have a bit more free time, I should probably grab a current version of Amaya and see how it fares (or, perhaps, some other 'masochist'-- see Tux's above -- would like to report some findings).