There's 2 things to consider when looking at those numbers:
1) The transition from the "garage geek" inventors like edison and tesla into a singinifcant majority of inventions being developed by huge corporations.
2) Corporations often do not report that they even have a patent on something until it goes into production - they are called "trade secrets" for a reason.
I do not think we are entering a "dark age" of technology, but rather, it's continuing to grow into areas where only corporations have the opportunities and they often keep their advances in-house only. Boeing and Raytheon come to mind here. As was mentioned earlier the fruit has pretty much been picked clean, and the opportunity for your typical geeky self-employed inventor becomes smaller every year. Tech is becoming so advanced that only large teams of technicians and scientists have a snowballs chance in hell of discovering the next lightbulb or pop-top soda can.
EDIT: come to think of it, I don't even think the big defense contractors need to patent their developements because most of them are highly classified. If you develop the next stealth bomber with a price tag of like 500 million per aircraft and it's going into production, the government provides the protection for your high-tech toys and gadgets. Patents are moot in such cases.