In an interview with Automotive News Lamborghini CEO Stephan Winkelmann declared that the 1,592 cars sold in 2004 were enough and that he has no intention of going beyond that number in 2005.
Winkelmann could have more than one reason for saying that.
Maybe Lamborghini is constrained by production capacity and isn’t even able of going beyond 2004 numbers.
Or maybe it’s a genuine desire for keeping the brand exclusive enough, with low volumes and sky-high prices, hoping to recoup investments by sharing engines and platforms with Audi (see for example the new S8 and the future R9 coupe).