Or maybe it's just because PD only have a limited amount of time and resources/staff in which to recreate these Premium cars?
Hence why important, ridiculously famous, fun to drive cars should all get first billing when it comes to being included, and included as premium. Cars that every single kid had on their bedroom wall fits this category. But I wouldn't tell PD what to include, as including some random derivative Japanese hatchback that will be forgotten in 5 years is their creative choice to make. It is my choice to buy their next game or not.
To produce them, they have to have access to IRL versions of cars to take detailed measurements and photos of these vehicles. It's obviously much easier to get hold of Japanese cars in Japan than it is some foreign exotic.
I believe PD would have stock photos, extensive measurements etc for many of the non-premium cars from work on past GTs etc... I'm not sure this is the critical issue explaining the car list. Other game titles (from America) have better quality models than GT5's standards, featuring loads of cars that haven't been put together in the developer's back yard. Forza has a vastly better selection of Ferrari, has Koenigsegg, has a good looking Countach etc... I'm not trying to bring Forza into things, just it is the obvious example
in how to manage a limited car count, in next to no dev time, and come out with a great compromise. Everything in game development is a compromise, but PD just don't seem to be making choices that can be explained. It is just plain odd.
Of course it comes down to man-hours, but it also comes down to creative choice and project management. They could have made a game with say, 300-400 premiums similar to a Forza title, but with a much more rounded out car list, such that every car was worthy of it's spot and even though there are less cars, it feels like there is more choice, because there are more
good choices.
But that is again getting into my personal taste with car lists. No matter one's taste in cars, it is clearly strange to have a new car not from GT4 (Countach) be modelled as a standard. I know it was from PSP, but if PD didn't think ahead at that point? Just how late in the game did any work proper on GT5 start?
Freight48
This is the most diluted, one-sided argument I've seen here in a long time. You sir, are ridiculous.
Aside from you possibly not picking up on my intentional overstatement to make a perfectly valid, yet somewhat frustrated point, care to elaborate? If you played an entirely different game to me, I can go on at length and great detail about the insurmountably huge flaws in the GT5 I played, but I think most of them have been adequately covered on this site...
premium or not.
... maybe even more than we can imagine... 
