sentences:  Available for limited time and only in select markets, on a restricted model range, these ""RS"" (and ""S"" models) models are wholly designed, developed and produced in-house by Audi AG's high performance private subsidiary company, Audi Sport GmbH, at its Neckarsulm factory.Unlike Audi "S" models whose interiors are well-furnished in order to retain the feel of sport luxury, the interior of Audi ""RS"" models are often spartan by comparison as the emphasis is more on track performance than luxury.The 2008 Audi RS 4 sold in Europe had lightweight racing-style front seats and roll-up windows for the rear doors, although its counterpart sold in the United States has luxurious power-adjustable front seats and power windows for all doors 2008 BMW M3 vs. 2007 Audi RS 4, 2008 M-B C63 AMG.