I can answer the thread question plain and simple. The reason that cars which were originally naturally aspirated as standard and have the option of being turbo'd but not intercooled, is so people can't buy the N/A Tuning and put an intercooler on for a turbo that isn't there. Make sense? The one error in this is the Audi S4 purchased new, which can only have N/A Tuning and no option of turbo, is N/A out the factory, yet strangely can get an intercooler.
That's a great observation mate, about the S4. My initial reaction was that the S4 was turbocharged standard out of the factory, but then realized you weren't talking about the '98 S4, but the '03 model, the only S4 of recent memory which hasn't had a turbocharger strapped to the exhaust manifold.
I did believe that in Gran Turismo 1, the only things that couldn't have intercoolers fitted were cars that generally had a lack of underbonnet space, and machines that were from hardcore naturally aspirated manufacturers(Honda, Chev, etc). The one thing that disappoints me about the whole tuning process in Gran Turismo is the clear lack of cars that you can perform a displacement increase for. Most muscle cars are well open to a larger crank and more cubic inches, but the Polyphony Digital team seem to think that Skylines are the only cars in the world that can be bumped from 2.6 to 2.8 litres, hehe.
The intercooler is clearly an error, but I remember some time ago, a guy in a VL Commodore had an intercooler fitted to his N/A car with no plumbing, just for show and had a BOV fitted to the intake piping. The idiot didn't realise that without a turbo, he'd never get the valve to open by simple atmospheric pressure and wasted his money. He also stuck the intercooler behind his front bar with zip ties and the thing was as loose as all buggery and rattled like hell. It was the funniest thing I'd ever seen but much more stupid than the kitted Civics, hehe.
Nice to see some people on this forum who know what a Commodore is. Most other people on other forums give you a blank look when you say Holden or XR8, hehe!