Comments have slowly collected in Part III and IV. In particular, Retriever has suggested that weather/climate/landscape may have influenced the dour East Anglian attitude as well.
One more blow to my theory. Popular historians have often linked geography with destiny. Michener was particularly fond of the notion. While they oversimplify, there is certainly something to that idea. Poland is a flat fertile area between Germany and Russia - that's it's history. Communication and trade on the Chesapeake was by boat, not by road - this shapes culture.
So, yeah - rain, fog, and swamps for a thousand years could influence one's outlook toward the grim. The cultural inheritance from the Saxons and the Danes is getting overlaid with other factors each time I look around. I still think the cultural idea has some juice, though, and I'll try to tie that up in Part V. Significantly, I'm not finding it easy to summarise into a post.