Many people mistake Base Models, to custom setup cars that practically every vehicle developer sells / releases for the public.
Custom Setup cars / car packs (for an example Ripple's Code 3 Pack) are based on Base Models.
You can not purchase Base Models (well you can, but unless you are a developer, they are useless to you), but they are essential for both the vehicle developer, and for our Liveries, because the Vehicle's templates are also bound to the base model.
So while base models shouldn't interest your everyday Joe who just wants to play with the cars, you still should be aware of them, and that what are the most used ones currently on the market.