To your question, where have all the inventors gone?, I have no statistics to offer, and I have not made a study of the question. I do, however, have some observations. For what it's worth:
1. I observe that the Expertise Bias is alive and well in America. Many are conditioned to leave invention to the "experts" and simply never entertain the idea that they themselves might get involved in the game. Somewhere in their schooling, they have lost the will for curiosity and the drive of imagination.
2. Patents are too expensive. I've filed two provisional patent applications, and they don't count for anything until you're ready to spend from $5K to $25K to get them converted to non-provisional status. For example, I have an invention right now that would revolutionize Internet discussion, making it considerably more efficient and useful, but I can't afford to get it patented---and much less to take it to market.
3. The value of a patent is only as high as one's ability to defend that patent in court. Just because you have the patent, it doesn't mean you have a war chest set aside to sue infringers. Nobody looks out for the little guy; you have to pay to play. So the whole system favors those with the most money.
4. The expense of taking a new product to market is ridiculous. If one wants to market alongside the big boys, chances are that he's going to have to bring in a financial partner who will demand a majority share in his company. And the same may be true simply for securing a patent. Having lost control of his invention/company, he may have little interest in inventing again.
5. "Sweat Equity"--the value infused into an invention by the countless hours of labor the inventor pours into it--has practically no value in the eyes of the sharkish venture capital community. They don't deem your idea to have value until it is backed with the cash necessary to get it to market. Thus, their cash (in their minds) brings the primary value to the invention and you and your invention become the minor partners immediately.
6. Protectionist laws and regulations limit the inventor's ability to work around the patent system and the venture capital model. For example, you can't just put up a web page asking for people to invest and offering something in return. Instead, you have to have a formal prospectus in compliance with the Securities Act of 1933, and you may only deal with investors who qualify as such in the eyes of the law. All this red tape serves to the advantage of the big boys who can afford it and it tends to discourage the little guy.
So just as you have noted John Dewey's triumph in the de-education of America, similar triumphs are inherent in the protectionist regulations involving inventions. The goal of institutional education in America (such as devised by Dewey et al) was simply to make a massive worker/consumer class out of the citizens. We were to learn how to work in their factories, and then to go shopping to purchase the products we make for them. Besides that, we are taught to entertain ourselves to the point of utter distraction from doing anything important, and we were taught that when we vote for one of the two approved candidates put forth for our approval, we have done a thing so spectacular as to defy explanation.
As the inventor of the Rule of Law Restoration, I can tell you that the public tends not to be impressed with inventions that solve problems about which they themselves complain! And as an inventor of certain improvements in the autobody repair industry, I can tell you that there is a strong bias against anything new, no matter how promising, effective, and profitable it may be. As a Bible investigator who researches Bible difficulties and common misunderstandings about the Bible, I can tell you that most Bible fans don't care about understanding the particulars of the very book they laud as the greatest ever written. And as the author of Character Not Included, I can tell you that few Americans are interested in any analysis or solution that requires them to read more than a single page in order to grasp it.
America is tired, lazy, disorganized, and distracted. And for the most part, so are her inventions of late. We don't even seem to care that our computers generally work so poorly and require so much maintenance and frustrating troubleshooting. Most of us just live with the inconvenience as if there simply were not a better way. We do not aspire to be better people ourselves, and we have no goals for the aspirations of the society in which we live---except, of course, to "exercise our right to vote", proudly putting into power a guy we hated last year, but whom we now deem to be a veritable saint compared to the guy the other party is running.
This is our dull society. And it remains dull mostly for our unwillingness to make it better. And we could most certainly make it considerably better if we were willing. But alas, that would require effort and thinking and trial and error and risk and invention and perhaps even some money. America the Great is apparently no contender in the face of such daunting obstacles as self correction presents. So we continue in our error. And those who care enough to devise solutions---they are the misfits. We are taught rather, that it is acceptable to complain, but not to attempt to fix anything.
Our very culture, therefore, is anathema to the spirit of invention.