Some really great points here!
To expand on some of them:
@rocketJobs that once opened the door to the middle class that are no longer available or are rapidly declining in numbers include: travel agents, bank tellers, switch board operators, auto workers, steel workers, accountants, sanitation workers (newer garbage trucks require a driver and a robotic arm), paper machine operators/setters, film processors and one day perhaps even airline pilots as drones become more advanced. But those that gained wealth through business acumen or simply inherited it by winning the reproductive lottery are doing better than ever.
While your first sentence is correct, it also bears stating that this is not a new phenomenon. Jobs have been eliminated by technology for generations. To use the "classic" economic example, look at buggy whip makers. Years ago there were thousands of people making buggy whips - not so today. They were obsoleted by technology. Look at farming - a statistic that I once heard was that at the turn of the century, one out of every ten people in America earned their living from farming (that includes the families of the actual farmers). Today, the number is something like one in 100. And, at the turn of the century, we were barely producing enough food to feed 200 million Americans. Today, with one-tenth of the farmers, we are producing enough food to feed 300 million people and exporting a third more! Why? Because of tractors, fertilizer, irrigation, etc. My grandfather worked in the coal mines. His job was to tend to the horses and mules that were used to pull the wagons through the mines and run the lifts. Bet he would have a tough time getting a job doing that today! So the obsoleting of jobs by technology has been going on for centuries.As for your second sentence, I don't know. Back in the day (not to long ago), we had "robber barons" and families like the Vanderbilt's, Carnegie's, J.P. Morgan, etc. who were desperately wealthy. I think that we tend to maybe have more "rich" families, but less "mega rich" families than in years gone by.Also, I think your point about preparation is right on. I read a statistic the other day that said that technology is evolving so quickly today that: 1)The amount of new technical information is doubling every two years. For students starting a 4 year technical college degree, this means that half of what they learn in in their first year of study will be outdated by their third year of study”; 2) The top ten in-demand jobs in 2010 - did not exist in 2004. The U.S. Department of Labor estimates that today’s learner will have 10-14 jobs . . . by the age of 38; and 3) We are currently preparing students for jobs that don’t yet exist . . . using technologies that haven’t been invented . . . in order to solve problems we don’t even know are problems yet. These authors go on to point out: "Though higher education is certainly about more than preparing students for jobs, technologies, and problems, one broader and exceptionally clear point emerges: We need to prepare students for what we can’t prepare them for."(Source).I think that, in order to re-expand the middle class we need to start with the youth and how they view education. Gone are the days when a child would "follow in his parents footsteps". By the time the child is old enough to follow the footsteps, the footsteps will be gone!