A lot of the early adopters like to go for the top phone available, which is the 5S. However, that phone isn't available. So most of the enthusiasts (like most of people on this forum) are waiting. In addition, 5Cs were likely well supplied (more than prior 5S/5/4S launches).
The 5C will likely do great in store, but there seems to be a lot of confusion among iPhone buyers in general right now. Once the reviews come out (which I believe will be favorable to both phones and surprisingly good for the 5C), things will get clearer. Remember, the look, feel and features of iOS7 will be identical among both phones, so many people sampling the phones in store may end up with a 5C given it is $100 cheaper.