When you say aircraft engines will come out of the 1930's, I completely agree. Regardless of the quality of 100LL, a typical new engine in a light, general aviation aircraft is really from a 1930's design and engineering mentality. They're huge displacement engines making low amounts of power. Compared to the amazing advances in automotive engines and turbine engines, the piston aircraft world has a long, long way to come to even reach 1970's technology.
The lawyers are likely to blame. Everything in aviation is overly expensive and has to be "certified" to be used. Right down to the $50 light bulbs that are $0.50 for your Chevrolet (and likely exactly the same) but the liability factor brings the price up. Because everything needs certification, it takes a long time to make it "airworthy" so it becomes easier to just keep on making what has worked and was certified before. This is to the point that if you invented and NDB, or a lycoming engine for that matter, it might not pass certification today because by today's engineering standards, it's old technology. It only keeps being used because it's proved technology. But this means little advancement.
Getting back to the topic of the thread, I have heard from a chemical engineer that 100LL is actually a very crude, poorly refined product compared to other fuels in use today. But since the aviation market demands old and low-refined fuels to go with its old style engines, they keep making it.
100LL's demise probably will cause a new era of conversion kits to allow most light aircraft to use 87 octane pump gas. Hopefully it becomes much cheaper and more easily accessible. As prices rise, the future may be with these diesel conversions.