Thanks for this link -- fascinating! I've been working on a Wikipedia article for Durham, a poem that straddles Old & Middle English (draft here, though far from finished) and encountering all this for the first time. I'd vaguely assumed that it was the suppression of Anglo-Saxon culture after the Conquest that did the trick, but obviously ordinary people continued to speak the language uninterrupted during the written record grows thin. I wish I knew more about Old English, but I guess one language at a time :)