l saw an article saying that the new 2010 Mercedes E class will have a 4 liter 6 cylinder chrystler engine.

Because they design a car and powertrain, test it, work the bugs out then put it into production all that takes a couple years to do. also it take time to make 200,000 cars which they start doing the year before

Simple,
Diamler still has a stake in Chrysler corp. l believe they kept between 9 and 12 % so they would still have the ability to share technologies like engines.