The "oil companies buying up the 100-mpg carburetor" myth is almost as old as Bigfoot. I don't know how it is in Britain, but here patents are published, and available for public inspection, no matter who owns them. I suppose an oil company could find an inventor and buy up his idea for a magic water-burning engine before he patented it, but they'd have to get there before the car companies did.

If you do some research, you will find that there have been many technologies invented to power automobiles. Almost all of them involve burning fuel in one way or another, but rotary engines, turbine engines, and forms of external combustion engines have been tried. None of them had everything needed to be marketable.

The basic concept of the jet engine was developed in the 1940s, and aside from radical improvements, still works pretty much the same way. Same for the internal combustion engine.

I can think of no other major industrial\technological "product" from the 1880's that has not been replaced, superseded, bypassed or otherwise rendered obsolete by now.

Well, granting your assumption that one can place a Model-A engine in the same category as the power plant of a BMW, I can think of a few right off the top of my head. Incandescent light bulbs. Stick-build housing. The telephone only recently got away from copper wires. The CD only replaced vinyl records in the past decade or so. I'm sure others here could add a few. If it works, don't fix it.