Price of Japanese cars being reduced in China is likely due to the enormous anti-Japanese sentiment wave that swept through the country last year.

As spwolf said, Lexus and Toyota have been pretty aggressive with pricing the new products, likely giving up some margins to do so. The easing of the yen will help restore some of those margins, and hopefully allow for some additional content, but again, they're not going to fluctuate prices with every movement of the yen.