David - that is so wrong in so many ways. The $1k computer is that cheap because they are low quality, cheaply made, made in extremely high volume, and essentially unregulated (as long as you don't electrocute your users and don't emit too much radio noise, anything else goes). (Oh - and when it fails, with depressing regularity, you throw it out and buy a new one.)
Automobiles are highly regulated and every slip in quality is broadcast by JD Power and similar ratings firms. For Porsche to have absorbed a ton of DOT, EPA, NHTSA, and similar agencies' regulations, added passive and active safety systems, tripled horsepower, and stayed even with the CPI is pretty impressive.
Looking at AX results from 9/10, in the "Stock" classes (xS and xSS), 9 of the fastest 10 are 1996 or later cars, and 24 of the fastest 30 are 1996 or later. In the Street Stock classes, 16 of the fastest 18 are since 1996.
If the newer cars aren't as good as the older ones, then why do the older cars have to be Modified or Improved in order to beat the stock new ones?
If your question is "Why isn't Porsche building street cars that can be used as race cars?", then I would say "How many PCASDR members actively race?". I think the answer is around 50-75 for real racers (POC/TT), maybe 125 if you include AX/DE. I believe our total membership is around 2000, which means that 4-6% of our club buys a Porsche to race it and the other 94-96% buy a Porsche for street driving. So do the math - how many times more Porsche racers would be needed for Porsche to move away from street cars to racers and get the same sales? Oh - and if they dropped to 4-6% of current production, then the prices could be similar to other "exotic" manufacturers like Lamborghini. $250K for a base model, anyone?