They don't build them like they used. They build them better. Automobiles manufactured today are better in every way than cars from the "good old days." They are faster, safer, more fuel efficient and more economical than those old cars we often pine for. If I were given a choice between a restored old car in perfect original condition and a run-of-the-mill new car as my daily driver, I would take the new car every time.
But the real question is: Why are new car engines so much better than old cars in terms of reliability, economy and environmental impact? A small part of the reason is design and materials, things like light-weight alloys, innovative head designs and tighter tolerances make modern engines better than old engines. But the single most important innovation in automobile engines is the wide spread use of Silicon. The same revolution in computer chip integrated circuits that drives the current communication revolution (and makes things like the Internet and this site possible) has made car engines better. Little computers are regulating the functions of your engine to such a fine degree that your engine runs more efficiently. Engine efficiency equals power, performance and economy.
Way back in the dark days of automobile design, as recently as the 1970's, the functions of the engine were controlled by vacuum lines, mechanical linkages and good wishes from the design staff. Old timers wax nostalgic over carburetors and distributors that they could adjust and repair with blacksmith's tools. They are horrified by today's high tech engine management systems that are best tuned with a lap top. But while the old systems would work, they were far from efficient.
As proof lets examine the most popular car engine in the world, the Chevrolet small block V8 engine. First sold in 1955, General Motors is still selling an engine that is basically the same design as the power plant of their largest cars and trucks. But the 1955 engine could never match the power, economy or clean burning of today's engine because it lacks the critical ignition functions of air/fuel mixture and ignition timing. Today's cars make power with environmental friendliness by insuring that the EXACT amount of air and fuel are delivered to the cylinders and that the resulting mix is sparked as EXACTLY the right moment. This is achieved through the use of computer controlled fuel injection and distributor less ignition that uses electronic signals from a crank position sensor.
Old cars are great for their style or the happy memories they evoke, but when you get right down to it they suck as transportation. Even the guys who lavish huge sums of money on old cars, restoring them beyond their original condition, will not drive them regularly because they really are not any more comfortable, easy to drive or powerful than a new car.
Do not get me wrong, I get a major woody for certain old cars. Largely because the sight of them transports me back to happy memories of my misspent youth. In particular are the cars from the mid 1960's until the very early 1970's, the cars that originally sparked the flames of automotive desire for me. And yes, I would like to one day own some really cool old cars. I just am not sure I want to rely on them for my daily ride to work.