Toronado got it correct. On both counts.
For those people who clamour for an option for driven sides: if you think it's a simple matter of just flipping the dashboard model, it really isn't. Because once you've done that, the textures would be jumbled up and you'll then have a helluva job reassigning them to the right parts/buttons. This doesn't take into account the various differences in the cabin between left- and right-hand drive variants of some models (the 370Z's handbrake, for example, stays on the same side of the central tunnel no matter which side the steering wheel is, so they would need to remodel a sizeable amount of the centre console, if not the entire dashboard). Multiply that extra effort by the 200+ premium cars in the game and it's easy to see why they didn't bother.
I'm still surprised that people are annoyed by this, because honestly, does it matter which side you're driving on, when you're on a track? Sure, it might take some getting used to, but how long does it take? Two, maybe three corners? An entire lap? Is it worth asking the developers, who already have their hands full modelling cars and tracks, not just for the DLCs, but for GT6 as well, to make left-hand drive models too?
Also, Polyphony generally takes hold of Japanese-spec cars to model, not because they're arrogant, or trying to push Japanese models of cars to gamers, or catering to specific markets, or because they couldn't care less, but because it saves time. They do fly out to model/collect information on some cars, yes -- sometimes because a car is still being developed, because it hasn't been on sale in Japan yet (or isn't going to be), or because it's a unique or vintage car that's located outside Japan. But why would they waste time going overseas just to model, say, a Volvo C30, when they can easily ring the local headquarters? It's cheaper, much less of a logistics nightmare and, most importantly, quicker, especially given their (sometimes) fastidious modelling techniques.
