Part of this might be due to the fact that the Camaro is a new model, whereas the Mustang is a mid-generation update (albeit a massive update, with big suspension improvements and a great leap forward in the interior).
Agreed, and a darn big "part of it" too....this is the early going for the Camaro and all the Camaro-fanboys are buying. In a year's time, Camaro sales will be poor (unless gas is a lot cheaper, which is not likely).