I think Lexus/Toyota does not want to experiment a new engine on a new car, especially a Lexus car. Toyota is not known for building engines, most of their good/high end engines are build or developed by Yamaha (most recently, the Altezza RS engine). Also, I think the Aluminum block will drive the price of the IS and GS up a bit too much, so in order to keep the price down, they decided to keep the old design. Like most magazine said, this is first generation of IS300/Altezza, it will take a while to really touch the BMW market share. I'll be surprise if anyone can have a first generation car that can touch the 3-series's market.