The main points have been hit on in here, but some things are being left out, and some are a little off.
Making cars reliable these days is much easier than it used to be. Building solid cooling systems and stronger parts is cheaper, and more info is available, plus cars are better designed for reliability from the start. The Supra is extremely reliable, as there have been many 1000HP Supras running stock block, stock head, stock head gasket, and stock radiator and fans (yes, really).
One of the primary factors is what these cars give up to make that power. No Supra is making 1000WHP on pump gas, unless you count E85, even that is a MAYBE. The highest, at my best guess, would be 600-650 on 93, and the turbo lag is unbearable for a mass-appeal car (non-car people like to buy high end exotics, too). Similarly, huge cams make an NA car more powerful, but make low-end driving much more difficult, and not ready for the inexperienced, unprepared, or lazy driver. A BIG cube engine increases driveability, but at the cost of gas mileage. Then, you can open the exhaust or intake up for better flow, but the car gets louder, and if you drop the cat, emission suffer, which are all big no-nos for production vehicles. Also, all of these cars are tuned. They use just the right combo of fuel and gas for maximum power, based on air density and temperature. In the case of a production car, they sacrifice a LOT of power by giving the car a VERY conservative tune (too much fuel), so that it can safely run in a Mexican summer or a Norway winter, along the beach or among the Alps. You can destroy an engine if it's perfect in one climate and fed too much air in another. Another factor is manufacturing costs. Tubular headers and a tightly-packaged intercooler are expensive, as are precision machined heads and all the other things that builders do.
The Veyron suffers from none of this.