It just seems that most American cars are automatics, so not everyone learns how to use a manual. There is definetely a knack to using a manual, once you get the hang of it, it's like riding a bike, you'll never forget it (or least I hope I won't), it's not actually the hardest skill to learn (although at first some people might take a while to get it). I don't see any reason why most American learner drivers couldn't learn to a manual.

Is the reason most American cars since the 50s or 60s have been automatics because American post-war consumer culture has been all about labour-saving? American cars (in fact America in general) had many gadgets and luxury innovations before ours did. In Europe, until recent years (the last 20 or so years), usually just the more luxurious cars like BMWs, Mercs and Jaguars used to have automatics.