I think there are two factors at play:

1.. They don't want to prematurely spend ad dollars waiting for just a month or so, before they start hitting the lots

AND

2. They probably figure, save the cash for models that will need it (tons of advertising), like the Journey and Avenger. The Challenger has tons of buzz even amongst those not crazed like us.

I'm sure there'll be some cash dropped at the launch and 6 months later after the buzz has died down.