Agreed, 80 isn't that high, it's just personal preference and habit, I guess.
I've driven in plenty of metros in the Midwest and the South, and always keep up with traffic. Not sure I've ever encountered all traffic going 80 in a dense metro area, maybe that's a regional thing? I was just in the Twin Cities and people were generally going 10 over the speed limit, which varied from 55 to 65.
And I cringe thinking about 80 through a 45 mph work zone area. That is how workers are killed.
South Dakota has some interesting signs that say 'Highway Workers, Give 'Em A Brake' with a construction worker image that are scattered about. in the winter season, they'll change to 'Snow Plows, Give 'Em A Brake' with an image of a snow plow. I'll have to try and get a pic of one of them sometime. They're pretty unique.